O2 UK-No Service-iPhone 4 Mobile or O2

Long story short. . . .
I have a iPhone 4. For a month now, I have had NO service from O2 UK in my region, both 3G and 2G networks. I made a complaint to O2, a case was opened, then closed after engineers found NOTHING wrong (yet other O2 customers are having problems). I was asked by O2 to swap the micro sim, which I have done. But still the problem is there. I contacted them today and told to either 1/ swap the sim AGAIN or it is the iPhone 4.
If I have had NO service from O2 in my region, yet it works perfectly elsewhere when I go into another region, it has to be O2.
But could it be the phone? I only ask as O2 have now put that doubt in my mind. Although I am pretty conveinced it is not the phone, but I wanted to check with others.
Message was edited by: Jonty71
Dell 1545 Inspiron - Windows 7 iPhone 4