Not providing correct adsl line speed

I pay for a 4Mb/s adsl line and have never received it this whole year. multiple calls have been made and complaints logged. technicians have come outonly to get the line to 3Mb/s and a week later it goes back to 2Mb/s. if Telkom cannot provide the line speed promised they should not be charging for it and be up front that they can only supply 2Mb/s instead of promising 4Mb/s. It is highly ********* and dishonest to charge for a service they cannot provide.