help me please

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if someone can help me it would be great. I had a working o2 xda. I tried to unlock it with the unlockers on the site and now it wont even work on o2 and I have just checked the imei number and its screwed ? what the hell have I done ??????
I can send and recieve txt on vodafone and tesco only. can not make or recieve calls on any network. This phone is not new 2nd hand is it possible I have screwed the imie number up or the last owner has barred it ? I have had it 3 weeks ?. is there anyway to find out if the phone is barred or if someone else has messed with the imie number ?./ As I said it was working fine .

cheers in advance