Faulty/Intermittent service with no explanation

We have been experiencing intermittent/no internet for the past month. The account details were previously in my fathers name and we had them changed to my name on 18 October. Before the account was transferred I had never experienced intermittent service, but after November 13 the problems started.<br> I called the customer helpline for 5 days and each time I got through I had to re-explain the issue to a new agent and have them tell me a different issue that could cause the problem, but to insist that there is nothing wrong with the line. Eventually on the 5th day I got through to a Zama at the technical department while I was at work, but she said I need to first run a self diagnostics test at home (which I had already done with another agent). I arranged for her to phone me at 8am the next day and she gave me her word she would do this first thing when she returned to work. However I was not expecting her to keep her word. I retried everything I had previously done to fix the internet and something must have happened because the internet was fine for another week but I never received a call. I am now back to the same problem and still don't have a clue what is wrong and how to fix