My local operator block my phone and now I can't use any operator

After vacations when I came back to my country I tried to used my sim card with my regular operator and It was impossible, so I try with different operators and nothing happened... after a couple of days I went to my first operator asking why I can't use my sim card. They told me it was blocked because was reported the phone as stolen. So, immediately I went to an Apple Store asking the way to prove the phone its mine, I went with my phone and my local ID hoping they would check by the serial number my information as the owner of the phone so with a print document of that, go to the operator and fix the problem. Unfortunately this Apple Store told me they work as dealers and they can do anything about it to check and prove I am the owner of the phone. I really need to fix this problem, I need to have a phone which I can call with.

Any idea?

Thanks in advance!