Welcome to the Community, I'm so sorry for the problems you're experiencing with your telephone service.
I've located your account to take a look at this and run some tests on the line from our end, we're not seeing any errors from our end though. Have you been able to test your handset on another phone line? Or your handset on another line? Just to rule it out as a potential cause of this problem.
If you've been able to do that, get in touch and I'll arrange for an engineer to come and take a closer look at this for you.
I'm just going to send you a private message as I would like to arrange for a technician to check your line so if you click on the purple envelope at the top right of the screen you will see another message from me with appointment times.