4Meg line slow

Unstable 4meg line use to get 350 - 400 mbps but now down to 50 - 80 mbps if I'm lucky but I still get billed for the line, After several calls and fault logging on the web no response, no mail no phone call noting. This is the worse service possible!! Unfortunately Telkom has the monopoly so they don't give a rats ass about customers as they know you have no choice but to swallow this bad service?? Was thinking of upgrading to 10Meg but with this I don't think so, what will I get then Telkom 10 Meg line maybe 150 mbps if you are lucky ??? Pathetic service....!! This is all the calls logged with no response what so ever: [Support #668326] #656632]. [Support #616673]