iPhone 7 Plus A1784 can not transfer to Verizon

I have an iPhone 7 Plus I purchased through AT&T. I paid of the phone and unlocked it with the plan to add it to my wife's account at Verizon. The employee at Verizon informed me that my phone the A1784 model will not work on the Verizon network. I did not know that I was being sold a hobbled phone through AT&T at the time I bought the phone several years ago. What can Apple do to resolve this issue?

Thank you,