Treated unfairly

I had a contract with Altech Netstar which ended in June 2017. A consultant from the company called me several times on renewal of the device I told them I dont want to renew with them. They never advised me to call in or write a cancellation letter. Two months later I received a statement saying I owed R310.08, I called the company spoke to Ms Marie-anne who is very rude. She told me she will get back to me for clarity as to who exactly called me. Despite the emails I have sent no response came my way and now the account has been handed to a collections company while I was awaiting response from her. I feel the company is being unfair to hand my account over to be paying so much chargers with an account that was still under investigations.