How to unlock Verizon’s iphone?

Hello. My pre owned iPhone is locked for Verizon. Apple support advise to contact Verizon. But Verizon’s told me that my iPhone is unlocked from their side. In Verizon’s forum I found out that this problem take place and can be solved by Apple with help of level 2 Support Technician or a Senior Level Advisor who will agree to forward a request to the Apple engineers who can fix it from their side.

It’s known that there is a law according to Verizon has now rights to lock iPhone.

so I get stuck in loop between Apple and Verizon.