bad service

I took out an account with mweb for a telkom adsl line in december 2014 and i am paying for 4 mb/psecond uncapped adsl line. i have been getting between 1.4 and 2 mb/ps for the past 8 months and almost every month i have been complaining about the slow speeds and every time i have been told they are working on it. its costing me R430 per month at mweb and R540 at telkom and i am not receiving the service i pay for. 2mb/ps costs R200 per month and i am paying R230 more. they told me before i took out the contract that i wil receive 4mb/ps and i have not once had that speed. the highest was recorded at 2.6mb/ps. im sick and tired of calling them and going to shops to resolve the problem. always excuses and waisting my time and money. FOR 8 MONTH!!!! please help me im so frustrated!!!