Possible to pay unpaid balance on second-hand phone in order to unlock the SIM?

My wife still had her old iPhone from AT&T. We live abroad now so I wanted to try to unlock it. I tried the unlocking form but received this answer:

"Your unlock request was denied because there's an unpaid balance linked to your device. You can submit a new request after the balance is paid in full."

The contract was actually not under her name, but her ex-employer's.

Is there still a way for me to find out how much the unpaid balance is and decide if I want to pay it myself, even though I am not the original contract holder?