Telkom poor service

Been with Telkom for 5 years due to no other broadband supplier. Had a 4meg uncapped line with very little hassle for long time. Then upgraded to 10meg in May of last year. The service was terrible from there on in. I have to call the call centre at least once a week regarding the line speed. Line speed right now is 1meg. Anyway, Techies pitch and tell me to change the router, then the line is dirty(?) then the exchange cannot handle the speed I pay for...... (How the hell can you sell it then??) Techie was on site last week and told me to put in a filter to clean up the line(???) that done, the change was a spectacular ZERO. I have no other option but to stay with Telkom as there's nothing else. What can I do to just get the service that I pay for? Begging, swearing screaming has no effect. If anyone has some other ideas on how to basically just get what I'm paying for, I would really appreciate it. Thank you