Money deducted whout reason EVERY TIME I recharge

I purchased this simcard last year (2015) in order to use in my old Blackberry as only a means of opening my home gate. I have a second (main) cellphone which I use for everyday use. Since the first time I purchased airtime to load on this line, money has been disappearing. Again, there is no reason why ANY money should be deducted off my account as I do not even use this line to make calls. I open my gate by phoning a number, it rings ONCE and no money should be charged. The only reason I charge my account is in order to have money available to phone my gate. I only load R5 at a time but loose this money every time! I expect to have all this money refunded to my account immediately. The word has spread far and wide about MTN *****ing money from their customers. Even though the amounts MTN has taken from me without reason if not millions, it is the principle. I will not stop here. Please make contact with me immediately. Ref # for MTN Complaint MTN REQ:*** - ***