MTN contract

I would like to lodge a complaint against Mondo,I took out MTN contract with them @R299 pm for simcard. the consultant by the name of Nicole Mariah advised me that my 1st billing will be in June for an amount of R 299 which I didn't have a problem with,June came surprisingly they double debited my account.I have been sending them emails to cancel the deal as it is inconviniencing me but with no luck no one is responding to my emails. Can someone please assist me to