IMPOSSIBLE TO CANCEL DATA STICK AT MTN

IMPOSSIBLE TO CANCEL DATA STICK CONTRACT. Trying to cancel data stick for the passed months seems to be impossible with MTN. Wrote several e-mails to customer care and phoned numerous times to try and speak to the cancellation department - they call themselves super heroes!!! There is no answer at the cancellation department and there is also NO OTHER WAY to cancel a contract. I even visited the MTN store at Cradle Stone Mall several times, but with no success!!! It seems impossible to cancel my data stick which is just ridiculous. I am forced to stop my debit order and use another service provider.