MTN *****ing money for XtraTime which was not subscribed to

I have been on prepaid for a while but in the last month MTN has deducted money as soon as I load airtime for XtraTime. I have NEVER activated this service on my number and don't WANT it. I check my airtime balance as well as data bundle daily and have never run out of airtime but sometimes top up with Data. I have just received a SMS telling me they have deducted for XtraTime . I never run out of airtime so how can they deduct money for a service that I did NOT request or even make use of? MTN are ******* as they are taking your airtime without your permission. How to CANCEL this service and get a refund? MTN is Pathetic!!!!! I've been with MTN for Many years, but now I've had enough. I'll be porting my number even if I have to sign up for a contract again. This is how FED UP I am with MTN