I live in the city of Swansea... Half a mile from the main BT exchange as the crow flies and the best BT can do is 20mb fibre!
I know we are covering old ground here but factory reset the device, set it back up with just your voip providers proxy, username and password and leave everything else as is and see if these issues are still present. (Don't connect it to your PSTN line, make and receive a call or two over voip) I would also plug your corded phone into the phone socket directly and check for any noise on the line itself.
If after all that you have no joy I would just replace the unit. I have tested an OBi202 with an OBiLINE against a Virgin Media PSTN line and that worked flawlessly.
Not sure if mare got an email notification about your reply to the thread, I moved the site over to a new server. I know he's been very busy, will drop him an email hopefully he will reply shortly.