Overbilled

I have been a Telkom customer for years now and this is not the first time I have been ******. I have a 2mb uncapped internet line and i'm paying almost R 600.00 rand a month what makes this worst is that I have 20% discount on my bill every mount!!! This has been happening for over 8 months now. To make matters worst every month on the 22nd I get a massage saying that im a negative impact on there lines and then I cant even connect to the internet so I have to use my afrihost account and pay lots of money just to used my afrihost capped account. My contract ended about 9 months ago and apparently I have a 12 month contract with them with 20% discount each month. the 20% is smaller then the vat added to the total -.- . Please give me feed back as soon as possible as I refuse to pay this much for the entry level internet and not even getting the service I am being overcharged for.