Not able to submit the unlock request
I have purchased non-contract locked iPhone SE from the AT&T store last year (09/Jul/2018) and I had the prepaid connection using that iPhone from 09/Jul/2018 onwards for about one year. Now I am planning to move out of US and would like to unlock my iPhone. When I try to submit the unlock request through https://www.att.com/deviceunlock/#/, I am getting the below error in Step 3.
"Looks like the IMEI number you entered doesn’t match an AT&T device. Try entering it again. Dial *#06# on your mobile phone to make sure you have the right IMEI.".
I have verified the IMEI number multiple times in my iphone, but not able to submit the unlock request successfully.
Please help me to resolve the issue and to unlock my iphone.