Unusable Internet service

I have a 10Mb ADSL line that has been stable at 6Mb for years. It has stopped working over the time that Afrihost CEO sent out an email apologising for the poor internet service. Yet despite migrating me to their new and improved network, and despite spending hours on phone calls with consultants that promise to followup and escalate the issue, I have been left with a line that mostly fails to connect, and when it does, only at 1Mb. I have an all inclusive bundle which means that the ISP is responsible for resolving the issue regardless! No reasonable customer can accept an issue like this for nearly two weeks!