Telkom vs Debt collection. unbelievable service , pathetic

i have taking a 2 year data contract with telkom in 2013 , 2 years had ended and I decided to go onto a month to month payment. Cancelled this month to month in October last year but the debits kept going. Customer agents assisting me agreed I should be getting debited Etc. This year 2018 telkom starts pushing for final payment from me however their agents are clueless on why or to give me a breakdown of the bill. Now Telkom has handed me over to debt collectors. How is a company that is so *********** still be allowed to do business ???? To date they refuse to answer calls , they refuse to call me back .