Internet slows down every few months

I am paying for a 4mb line and when I do speed tests I get less than 1mb download. This has happened multiple times since I have been with Telkom, each time it takes weeks to resolve and its is mostly just a congested node. Logging a fault on their systems doesn't help, I always end up back on Hello Peter. I work from home as a web developer and this effects my income. Please Telkom, help me solve this quickly.