Motorolla razr....?

I found a motorolla razr at a gas station. it's carrier was t-mobile so i decided to return it there, the lady was very nice and told us to keep it. I have cingular so i said let me just change the SIM card and now its asking for a subsidy code....the problem is that we cant go to t-mobile to get the code because the lady told us not to because she checked whose it was and he had reported it stolen...so we are liable for sue and the code problem was going on even before i put in my SIM card...what can i do???