Impossible to cancel a contract when it has ended

MTN South Africa is a ZERO star experience. After your contract is up, it is basically IMPOSSIBLE to cancel it. I emailed them several times, called them several times, went into a physical store and they just don't cancel it. They were taking money from my account every month even though the contract ended and I was no longer using it, so I cancelled their debit order, and they logged several non-payments against my credit report. They should not be allowed to do this, avoid MTN at all costs!