Incompetence

I had a DSTV account for close to 20 years.The end of November I cancelled it duento the fact that all their programs is a repeat.I phoned and let them know a week before the end of November that I am going to end my account.The lady said as its a month to month account I dont need to worry,they will just stop the account.The first week in january I noticed I own R98 rand,I phoned and the lady informed me that the account was still running 2 days into December so I need to pay the outstanding ammount and then the account will be closed.I paid the R98 and according to my knowledge the account was closed.Now a debt collector informed me that Multichoice appointed them to collect another R100+.How do you explain that if I dint even have a decoder or account anymore.Please sort out your accounts,cause if I get a bad credit due to your incompetence I will take it further.