Xseries :: X6 "Connection Errors" When On A Call?

For the last few weeks each time I send/receive calls I am regularly cut off with the statement "Connection Error" appearing in the window. This has occurred sometimes within the first minute of a call and other times after 20 minutes, at the moment its every call. It also occasionally restarts itself (telling me, but then only giving me the option to say OK).

I have been to my network provider (3) who were appallingly bad and sent me pillar to post and back again so I changed provider to 02 and have spent quite a bit of time with their Guru who has performed a software update and a reset without success. When he tried to do something else the computer failed the action several times and he said the only thing he could do was send it away but because I am on PAYG they wont for me.