Unable to unlock U102aa flip phone, KiaOS 2.5.3

I'm trying to unlock my U102AA phone running KiaOS 2.5.3. I've been using it for years with a prepaid ATT account, and it is paid for. I spoke with ATT Customer service 3 times, and they confirm it is eligible to be unlocked. I've tried the unlock device link using a laptop, but I get rejected since my name and phone number for some reason do not match in what's in your system. Of course when I log in to my prepaid account I can verify my name and number that ATT has on record. In my 3rd call to customer service, they gave me a phone number for the manufacturer, but the manufacturer will not unlock the phone. I've spent several hours trying to unlock. It should not be that difficult - please help.