Unlocking a pre-paid phone. No longer have an ATT account

We have an iPhone 7 Plus that is locked to the ATT network. The phone had been used on a prepaid ATT account for 5 months, and is now serviced by a different provider that utilizes ATT network/sim. I understand that ATT prepaid phones are locked until they reach 6 months of pre-paid service. This phone belongs to my senior father.

What are my options to having this phone unlocked? Can I pay for one additional month (to reach 6 months minimum) of pre-paid service to qualify for unlocking?

I've gone into the my local ATT store, but they are "unable to assist" and recommend that I call ATT Prepaid customer support. When I call Prepaid, the automated system does not provide me with any option to speak with a human and hangs up. Please advise. TIA