Random number is not refreshed on submit - html

Question

I have a random number generator (for voucher numbers), but when I click the button, a new random number is not shown. Can anyone help please?
This is my controller that generates the random number:
static Random random = new Random();
public List<string> RandomVouchers()
{
int vouchersToGenerate = 1;
int lengthOfVoucher = 10;
List<string> generatedVouchers = new List<string>();
char[] keys = "ABCDEFGHIJKLMNOPQRSTUVWXYZ01234567890".ToCharArray();
while (generatedVouchers.Count < vouchersToGenerate)
{
string voucher = GenerateVoucher(keys, lengthOfVoucher);
if (!generatedVouchers.Contains(voucher))
{
generatedVouchers.Add(voucher);
return generatedVouchers;
}
}
return generatedVouchers;
}
private static string GenerateVoucher(char[] keys, int lengthOfVoucher)
{
return Enumerable
.Range(1, lengthOfVoucher) // for(i.. )
.Select(k => keys[random.Next(0, keys.Length - 1)]) // generate a new random char
.Aggregate("", (e, c) => e + c); // join into a string
}
This is the orders page :
<div id="vouchercode" style="display:none">
<ul>
#foreach (string strVouchers in ViewBag.Vouchers)
{
<li>#strVouchers</li>
}
</ul></div>
<button id="getvoucher">GenerateVoucher</button>
This is javascript code:
<script type="text/javascript">
$(function () {
$("#getvoucher").click(function () {
$("#vouchercode").dialog({
width: 460,
height: 200,
modal: true,
});
});
});