Money being deducted off my airtime,- no reason

I would like to report that I have 3 lines (numbers) on my top up contract with MTN, and I have noticed that over the months systematically money has been deducted off of my airtime without the phones being used. it is not a lot at a time and that is why it was not picked up, but it seems like every 10 to 15 minutes, amounts of about between 10c to 20c is being deducted. I have called the call centre, held on for more than an hour, eventually got through to someone that said there are no subscribsitions on any of the numbers , and they cant see why money is being deducted, but they will look into it,,,, still waiting... I eventually went onto MTN's website and reported it as ***** , on Saturday 27th June 2015,,,,, to date no response from MTN.... we cant cancel our contracts as we have a year left on each of the numbers, but I have been with MTN for about 15 years, and just wonder how much has been ****** from me in this way??<br> Can someone please get back to me and explain WHY this is happening and REPLACE the airtime / money taken off over the months. I know of more than 100 people that are complaining about the same thing, but are also not getting answers from MTN's callcentre!