Disappointed in mtn

I am really disappointed in MTN. I had a contract that ended a while ago. Well at least I thought that it ended cause I stopped recieving my monthly statements. But out of the blue more than 6 months down the line they sent me a statement claiming I owe them money! And not only that but they listed it on my credit report :(. To add salt to the wound their customer care consultant decided to stop replying to my emails when I asked 'why i stopped recieving my monthly statements.' Its really sad for me cause I don't even have the sim card anymore and I am being charged for something that I didn't even use.