Incorrect billing bt Telkom

I have been a loyal customer with telkom for so many years. I had an ADSL which I was happy about. It was costing around 400 a month. Until they told me they are getting rid of copper, my nightmare started. They "upgraded" my line to wireless and they told me nothing will change. I noticed immediately that my data was finishing in a week. I tried quirying this, I was told its because of the higher speed I m getting. Third month on this new wireless connection my bill is R9000. 00. I went to their stores disputing the bill asking for explanation. No one could explain it. I have desputed my bill more than 5 times but I never got any explanation. Instead of explaning my bill they reduced it to R5000. 00 which they insist I must pay. I am still desputing the bill on my account. Now they are enroute to blacklisting my name which I believe its unfairly as they cant explain their billing. I am frustrated as we speak. They are taking their customers for a ride. I would really appreciate if I can get an explanation from them.