Paying for a 10Mb/s line, only syncing at 5Mb/s

I upgraded to a 10Mb/s line a year back. All was good, the line was syncing at 10MB/s and I was happy. A few months later, I noticed a drop in the line speed. I noticed that the line sync decreased from 10Mb/s to 5Mb/s. I logged a ton of calls to Telkom who said that they would sort the issue out. I get frustrating SMS's a day later saying that the fault has been fixed, which it never is. I don't see why I should pay for something I do not get. Plenty of options for wireless broadband nowadays, let alone fiber. If this issue does not get resolved, you will have lost me as a customer.