My Galaxy S3 (O2 network and 6 months old) has lost its 3G connection. Wifi works fine. I have not adjusted any settings and the only thing different is a new front screen protector. I have removed battery, removed SIM, checked all settings but still not working. Any ideas or a case of return to O2 shop and test another SIM card?
It might be worth phoning O2 to see if they've cut you off. Errors do occur!
(For example, someone might have reported their phone stolen and asked O2 to ensure that it can't be used. A single erroneous keystroke could have resulted in your number being disconnected instead of the correct one).
Could call and everything but no 3G. Did as up you suggested n contacted O2. They went thru some set up changes with me and 3G returned. Unsure what happened by they say these things happen. Cheers Buenchico