Canceling contract with mtn is a mission

Cancelling a contract with MTN is a mission shame. My contract expired I called them to cancel it the lady told me I was supposed to cancel it a month before, I said it's fine cancel it now and guess what I just received a bill of R565 and I used to pay R160 for data. I regret taking a contract with MTN and I don't advise anyone to take a contract with them. MTN is robbing people shame. I called the customer care now and their telling me that because my contract expired and I didn't call in time that R565 is for the 7gig of data that I used what a wow. Your service is bull****