Adsl faulty for months

I've been battling with Telkom for about 4 months regarding my adsl line. We have had stable adsl since February 2015 with a sync speed of 1.6mbps to the exchange up until 4 months ago. Then the line started to drop and the sync speed dropped to 1.2 maps. It eventually got worse until the sync speed was sitting at 40kbps! Multiple faults were logged and I was eventually told that I'm to far from the exchange. I understand that I'm far from the exchange but it doesn't explain how I can have 1.6mbps for nearly a year and then all of a sudden nearly nothing. Then all of a sudden Telkom contracts a company to replace about 1km of copper cable. Why do that if distance is the supposed problem?! I spoke to the technician after the installation and he said they can't understand it but the new cable made no difference at all! He even tested my line right in front of me and showed me it was faulty but I get an sms from telkom saying the line is fixed and fine. It's not!!!! I want this problem resolved properly or a refund for at least 4 months of unusable service.