Bad service

I had an contract with Altech for 24 months which expired in April 2015. The letter for cancellation was done and they acknowledged receipt. Then an agent from their call center called asking if i do not want to extend my contract and i said no but i agreed on extending the Data bundles for another 24 months fro R99 a month. on the 10 of April the line was cut and i contacted Altech no one could assist me i Spoke to different people. first person i spoke to was Tshepo. He promised that they would come back to me with in 24 hours and if that didn't happen i must ask for a manager which was the case. no one called and on the monday the 13 i spoke to Elias and he refused to put me through to a manager. a week later after contacting a lot of people i was called by the lady called Roxon and informed me that the contract was terminated and asked if i wanted to activate it or keep it like that i said keep it like that. since then i have been getting emails from Altech saying i owe them money. every month they deduct money from my bank account. i have tried calling them explaining what happened but they refuse to assist saying i should pay R500 to cancel the contract as it was reconnected