atrocious service - Incorrect billing for over 8 months - logged multiple calls and still no resolve

Atrocious service - Incorrect billing for 8 months, logged multiple calls and tried to call the call centre (Waited 67.5min) before i hung up. i have paid the average however the statements are always incorrect. i even uploaded my meter readings and guess what they still send me the incorrect meter reading with estimated billing. they were cheeky enough to send me a pre-termination letter and charged me for the letter :-( ... they are absolutely useless