What Should I Do?

I often save file in my mobile phone.It is convenient to have usb cable where ever you go.I use usb cable to transfer files from computer to my mobile phone. I save pictures and games also.I notice my phone often hang so I move the files and games to usb. I think months past mother send me a message that she cannot call me.I was amazed because my mobile phone is okay.I borrow my friend mobile phone to dial my number unfortunately it was true.My number is always busy.I bring my phone to motorola repair center but they told me it is not defective. I go home. I scan it thinking that it was infected by virus.It was detected two virus and removed easily.I borrow my friend mobile phone again.I try if the problem was already fixed.I feel distress because my mobile number is still unreachable :-( oh..! I don't want to buy a new mobile phone.I am out of budget for new gadgets.I don't know what shoud I do.My last option is to visit network provider office or just change my sim card...