Horrible Service

I have a problem with Telkom, I had a contract with them for past 2 years and I was paying every month until that 24 months ended. However few days ago I got sms saying i'm owing them arrears so I went to inquire from them and they said I didn't cancel my contract after that 24 months. The contract was supposed to end automatically now I really don't understand... I really don't recommend it.