BILLING ON A CANCLLED ACCOUNT

I cancelled a contract in May 2015 bacause i had opened a new account with them,but i still get invoices for the account.the number has been inaction since last year and i cancelled the contract because of billing problems.There are always amounts due in accounts i dont know how they bill and not bill the otheer months.How do you get billed for an account you closed at a store? so when they were investigating the case the lady said they cannot see the payment from their side and that i should send a bank statement,i asked her if they are not using the same system with the store as i had seen all this in their system and she couldnt answer.TELKOM / 8TA PLEASE SORT THIS OUT