Problems with Unlock request on AT&T website - non-AT&T customer

I purchased a LG G8 from Swappa with a clean IMEI.  I have checked the IMEI on several websites and it is not on a Blacklist.  I have been attempting to use the AT&T unlock portal to unlock the device.  I submitted the IMEI and my personal information.  Each time I use the confirmation link.  After about a day, I ALWAYS get an email saying that I did NOT confirm my email address and my request has been canceled.

So, I called AT&T customer service number and talked to a representative.  I informed the representative I was not the original owner, and he told me I would have to use the portal.  I explained to him the problem, and he started taking down some information.  He tried to submit an unlock requsest to see if how far he could get, he stated he recieve an "unknown error" and that the original owner would have to call and give information so they could do an "Override".  I stated that I would get in touch with the original owner.

Long story short, although the original owner appeared cooperative he is no long communicating with me.

I would like to know how to escalate this issue.  The phone is clean, and the portal isn't rejecting the IMEI, but it appears to be giving an unknown error.  As the phone is paid off, and not in service of a current AT&T phone number, I should have the right to unlock the phone, but AT&T is not giving me an alternative to using the portal even though it is giving an errorneous cancellation each time.

Thanks for your time.