If you don't mind me asking, as I have spotted something within your original message to us.
In reply to:
Also the first time i spoke to O2, they told me to try a stop and start request with BT
Did you ever do this?
Did it ever get completed?
A stop and start order is a PSTN (Voice line) order normally used as part of a change to some aspect of your voice service. This is one of the things that causes the dreaded PSTN CEASE.
In effect, the STOP removes every service from the line, including broadband. The start order (both are done as part of a single combined order) will restart all services in the PSTN providers control. As the Broadband is not in their control, this isn't restarted and only the Broadband provider can do this.
On some occasions, the Broadband provider is not notified about the PSTN CEASE, and to them it looks like the service is still in place.
Although speculation at this stage, there are hints here that this is what is happening. It will however depend on if the stop and start ever took place at your request, or if one took place for your reasons which you may not be immediately aware about.
Can you think of anything else recently that you had to contact BT about your voice line for?