rereigster my bb!

Here is my problem, I bought a blackberry curve 8900 from UK (was locked to O2 network), I had it unlocked from a site and now I can receive calls through my GSM carrier, the thing is when I tried registering my BB I get a �The blackberry is registered with a different service provider. Please re-register this blackberry and verify the URL matches the one provided by your service provider.� How can I do that:confused:? Do I have to unlock it again:confused::confused:? Plzzzzzz help:(