Very bad service

I has been 3 week now. I am paying for a 4mbps line at mweb and telkom for almost a year now. the line was working fine up an till 3 week ago. my line drop to 2 mbps. so i got in touch with mweb because they are managing my telkom line. mweb inform me that a tech will phone me and one did(Brian). We did some test and he told me he is going to give it to over to telkom. i waited 2 days and telkom send someone out to my premises and the guy from telkom said that they have dropped my line to a 2 mbps and that i should phone mweb and let them also drop my subscription to 2 mbps. I ask the guy from telkom why they did this and he said that the coper wire is unstable and there is nothing they can do. My question to him was then: Why was my line OK for 11 Months and now all of a sudden it is unstable? He could not give me a strait answer and he said that he will go to the box and test the line their and he never came back. I want what i am paying for. My internet just getting slower. at this moment im am at 0.39mbps that is unacceptable.