This isnt really a troubleshooting step for you phone, but an option that may be available to you depending on where your travels have taken you is that you can actually purchase sim cards for a reasonable price that will allow your phone to work using the towers available, just something to think about
-----Also make sure that in your settings that you have the roaming settings set to Voice & Data as well as your international roaming setting turned on, purchasing a local sim card should resolve this issue if verizon has unlocked that service, which from what you have said it sounds like they did, so next i would just go purchase a sim card, see if that works, if/when it does contact verizon to straighten things out