Data subscription

My name is Thabo I opened an account at Mr price maponya an I was offered airtime n data for 150 every month then went n canceled it because they **** they were only loading data, I just found out that they didn't cancek the subscription an they say I owe them 800 now kindly assist me with this situation, I don't want their data subscription anymore because I pay every month but the account goes up, I only bought clothes for R600 while ago paying every month but they say I owe them 800 because of data subscription that I took n canceled it, only to find out that it's still active