GET command not working

I have a form that is supposed to display the current data in the fields like this:

Name: Jurgen

Phone: 988484

Email:knkan@lmlms

and then the user can make changes and click on update and it would change the data in the table.

Now the update button works and it changes the information but the Original Data is not displaying in the fields when the form opens.

My code is: (iv tried everything so please let me know what i did wrong in my code, thank you so much)

$mode = $_GET['mode'];
$checkSql="select count(id) as eCount from address where ext = " . $_POST['ext'];
$result = mysql_query($checkSql);
$row = mysql_fetch_assoc($result);


if($row['eCount'] > 0) {
echo  "Extension Number already exists";
$mode = 'add';
}
if($row['eCount'] == 999){
$disable = 1;
}
switch($mode){
case 'add': 
?>
<h2>Add Contact</h2>
<form name="form1" action="<?=$_SERVER['PHP_SELF'];?>?mode=added" method="post">
<div align="center"><table class="searchable">
<tr><td>Extension:</td><td><div align="center">
<input type="text" name="ext" required />
<span class="error">* <?php echo $nameErr;?></span>
</div></td></tr>
<tr><td>Name:</td><td><div align="center">
<input type="text" name="name" required />
<span class="error">* <?php echo $nameErr;?></span>
</div></td></tr>
<tr><td>Department:</td><td><div align="center"><select name="department" required>
            <option value="ADMIN">ADMIN</option>
            <option value="AFTER-SALES DIRECTOR">AFTER-SALES DIRECTOR</option>
            <option value="ALPINE DEALER PRINCIPAL">ALPINE DEALER PRINCIPAL</option>
            <option value="AUTO ARMOUR/AUTO ENHANCE - FITMENT CENTRE (Smash and Grab)">AUTO ARMOUR/AUTO ENHANCE - FITMENT CENTRE (Smash and Grab </option>
            <option value="BANDIT-VW">BANDIT-VW</option>
            <option value="BOOKINGS VW">BOOKINGS VW</option>
            <option value="DRIVEWAY/WASHBAYS">DRIVEWAY/WASHBAYS</option>
            <option value="FINANCE AND INSURANCE">FINANCE AND INSURANCE</option>
            <option value="IT DEPARTMENT">IT DEPARTMENT</option>
            <option value="MARKETING DEPARTMENT">MARKETING DEPARTMENT</option>
            <option value="MASTER CARS">MASTER CARS</option>
            <option value="MAYOR OF PINETOWN">MAYOR OF PINETOWN</option>
            <option value="NEW CAR PREP DEPARTMENT">NEW CAR PREP DEPARMENT</option> 
            <option value="NUMBER PLATES">NUMBER PLATES</option>
            <option value="PANELBEATER - EASIFIX - CAR CARE">PANELBEATER - EASIFIX - CAR CARE</option>
            <option value="PARTS">PARTS</option>
            <option value="PARTS DISPATCH">PARTS DISPATCH</option>
            <option value="PARTS TELESALES">PARTS TELLESALES</option>
            <option value="USED CAR PREP AND ORDERS">USED CAR PREP AND ORDERS</option>
            <option value="VW NEW CARS ADMIN AND STOCK CONTROL">VW NEW CARS ADMIN AND STOCK CONTROL</option>
            <option value="VW NEW VEHICLE SHOWROOM">VW NEW VEHICLE SHOWROOM</option>
            <option value="VW SERVICE ADVISORS">VW SERVICE ADVISORS</option>
            <option value="VW WORKSHOP">VW WORKSHOP</option>
            <option value="VW WORKSHOP FOREMEN">VW WORKSHOP FOREMEN</option>
            <option value="WARRANTY & CLAIMS">WARRANTY & CLAIMS</option>
            <option value="WORKSHOP DRIVERS">WORKSHOP DRIVERS</option>
    </select>
<span class="error">* <?php echo $nameErr;?></span>
</div></td></tr>
<tr><td>Email:</td><td><div align="center">
<input type="text" name="email" pattern="[a-z0-9._%+-]+@[a-z0-9.-]+.[a-z]{2,3}$" name="email" title="Example: user@company.co.za" required/>
<span class="error">* <?php echo $nameErr;?></span>
</div></td></tr>
<tr><td>Cellphone:</td><td><div align="center">
<input type="text" name="phone" />
</div></td></tr>
<tr><td colspan="2" align="center"><a href="javascript:history.go(-1);">Back</a> | <input name="Submit" type="submit" id="Submit" value="Add New Contact" <?php if($disable ==1){?>disabled<?php } ?>/></td></tr>
<input type="hidden" name="mode" value="added">
</table>
</div>
</form>
<?php
break;
case 'added':
$name = $_POST['name'];
$phone = $_POST['phone'];
$email = $_POST['email'];
$department = $_POST['department'];
$ext = $_POST ['ext'];
$sql = "INSERT INTO address (ext, name, department ,email, phone) VALUES ('" . $ext . "','" . $name . "','" . $department . "', '" . $email . "', '" . $phone . "')";
mysql_query($sql);
header('location: ' . $_SERVER['PHP_SELF']);
break;
case 'edit':
?>
<h2>Editing: <?php echo $_GET["ext"]; ?></h2>

<form name="form1" action="<?=$_SERVER['PHP_SELF'];?>?mode=edited" method="post">
<table width="399" class="searchable">
<tr><td width="87">Extension Number:</td>
<td width="551"><div align="center">
<input type="text" value="<?=$_GET['ext']?>" name="ext" />
</div></td></tr>
<tr><td>Name:</td><td><div align="center">
<input type="text" value="<?=$_GET['name'];?>" name="name" />
</div></td></tr>
<tr><td>Email:</td><td><div align="center">
<input type="text" value="<?=$_GET['email'];?>" name="email" />
</div></td></tr>
<tr><td>Cellphone:</td><td><div align="center">
<input type="text" value="<?=$_GET['phone'];?>" name="phone" />
</div></td></tr>
<tr><td colspan="2" align="center"><a href="javascript:history.go(-1);">Back</a> |<input name="Submit" type="submit" value="Save Changes" /></td></tr>
<input type="hidden" name="mode" value="edited">
<input type="hidden" name="id" value="<?=$_GET['id'];?>">
</table>
</form>
<?php 
break;

case 'edited':
$name = $_POST['name'];
$phone = $_POST['phone'];
$email = $_POST['email'];
$Ext = $_POST ['Ext'];
$id = $_POST['id'];
$sql = "UPDATE address SET name = '" . $name ."', phone = '" . $phone . "', email = '" . $email . "', Ext = '" . $Ext . "' WHERE id = '" . $id . "'";
mysql_query($sql);
header('location: ' . $_SERVER['PHP_SELF']);
break;