Unable to cancel my data contract

MTN seem to use devious methods to keep a person from cancelling a data contract. I was not able to cancel at a MTN store over the weekend as 'retentions don't work on weekends'. The call center is hopeless - there is no option to speak to an operator or to cancel. Mails sent to the customer care email address and the retentions email address are simply not rep**** to. Very frustrating!!