Device Unlock Form Does Not Recognize My Phone

Greetings,

I have paid all the installment payments for my phone (Galaxy Note3). Since I will outside the states for more than three years I have decided to cancel my account with AT&T. Now I want to unlock my phone but the website does not recongize my phone's IMEI. It says "We do not have a record of the IMEI you entered. Please verify the IMEI entered is correct by dialing *#06# on your device." Is there anyway to surpass this issue. AT&T has already canceled my number and I cannot contact them either with live chat or with their number. I also cannot visit any of their branches because there is no one where I am.