Mtn Debit order months after cancellation

I have sent numerous emails to customer care to cancell my husbands cellphone number, the confrimed rhat rhe contract has been cancelled but still a debit order goes of every month. We tried sropping it at rhe bank and then they just put in a higher amount, how can they co nfirmed it has been cancelled and still they debit his account seveeal months after. They have very bad customer service