Slow ADSL due to congested DSLAM

Our 4Mbps ADSL line speed consistently yields between 0.1Mbps and 0.4Mbps, very occasionally peaking at 1Mbps. When reporting it, Telkom's response is to blame the ISP. However, we have PROVED that it is not our ISP as follows:<br> 1) Test speed at our premises, speed = 0.3Mbps. Take our modem to my sister's house 5km away and test the speed on her ADSL line using a) OUR MODEM and b) OUR ISP and we get 3.6Mbps!! Come straight back to our house and we get 0.3Mbps.<br> 2) We have also tried a second ISP at our house, and also only get the same slow speeds.<br> The test using our modem and our ISP on another ADSL line PROVES that it is not our modem or ISP. We have reported the slow ADSL speed to Telkom on numerous occasions, the latest being 3 Oct (ref 84CNK031015). Telkom have verified that the line itself is good. Although everything points to a congested DSLAM, Telkom will not admit to this nor have they made any attempt to rectify the matter. We continue to pay for 4Mbps and get worse than dial-up speeds. PLEASE can someone from Telkom attend to this matter urgently.