Hi @Anonymous and Welcome to the Community Forum,
Have you spoken to O2 Customer Services via dialling 202 and if so what did they say ?
If your not getting reasonable assistance to obtain the deposit back ,and you've met the criteria to get it back then here is the official complaint form :
http://www.o2.co.uk/how-to-complain/complainRegarding issues with signal.
Is this happening at home or everywhere ?
As a process of elimination can you try your SIM card in another phone. And try an O2 Payg SIM card in the phone. This will help to highlight if it's your phone or SIM card at fault.
Put your full postcode here
http://status.o2.co.uk/ to see if your masts are at fault. Look also at the planned maintenance tab at the bottom of that page.
Here is a Self Help thread :
http://community.o2.co.uk/t5/Pay-Monthly-and-Pay-Go/Self-help-guide-Is-the-network-down-for-me-or-everyone/m-p/593752#M59833Are other people in your area on O2 having similar issues ? If so and the Service Status page is showing as good then download the MYNETWORK App to report the masts.
When a person comes here asking for advice on networks we always suggest trying out a Payg SIM card to test out signal where they Live, Work and commute as the online network maps are for indication only.
O2 states that their Network is not fault free and is not available everywhere which is why we advise trying them out via the Payg SIM cards.
Also you may be suffering from Mast Congestion which is something you cannot do anything about.
O2 link on itemised bills and accessing them
http://service.o2.co.uk/IQ/SRVS/CGI-BIN/WEBCGI.EXE?New,Kb=Companion,question=ref(User):str(Mobile),CASE=22383Let us know how you get on.