ADSL line still slow after three months

I have complained a few times about my ADSL line speed, but NOBODY at Telkom actually cares to get back to me or fix the problem. I am on a 4 mbs line, but the last few months my average line speed was between 0.36 and 1.76 mbs, not near 4mbs. I have replaced my indoor cabling, my DSL filter as well as my modem. I still get the same speed. I have tested with my wi-fi as well as ethernet cable. The modem connects at 3.77mbs to the exchange, but I get these low speeds. Can somebody please help me to get this sorted out. I have logged complaints with the call center, but it never gets resolved and I never get contacted. When they test the line they say that there is no faults on the line.