Slow download speed

Every week I have to phone Telkom costomer care line because of slow download speed. Everytime I phone the technical staff does something and the speed comes right but the next week the same issue. Every time I tell them that its a recurring issue and they need to find the problem they scare me off with their threats of unnecesary call out fee. Clearly there is a issue and I cant believe that telkom cant resolve it, I have stood by telkom for many years after a lot of people tell me to move my isp.