Last year I had no landline for about 5 weeks. Every Friday they closed the complaint without explanation although nothing was fixed. By about week 5 for the first time they texted by mobile to say it was all fixed (and it was) - no compensation of course. It seems to be a customer service pattern with many companies that presumably dishonest horrible staff close complaints when all that person has done is sent an unsatisfactory reply back to the customer - we see it again and again with lots of different companies.
I really hope your issue has now been found. In my case it seems to be have been a series of issues. We had a faulty Fibre to Cabinet fault fixed at one point too. I find the constant loop of doom so annoying though.
Hope your internet works now 🙂