MTN airtime and data disappeared

My MTN airtime and data is disappearing as soon I load it. For more than a year I have been doing very well and been happy with purchasing my 160.00 airtime and converting to a 1Gig bundle and getting a free gig. For the past month or so, my 2 gig bundle has been depleted in 5 days! I loaded 15.00 airtime on Friday 17th July and within a few minutes it was gone. I called the call centre and they told me switch all open apps off. I did so and loaded 12,00 airtime on Friday evening. Within 4 minutes it was GONE! Holding on at the call centre is a mission. When I did get through to an advisor, I found myself being transferred between customer service and the technical team - on a call which lasted almost an hour! Is there someone at MTN who can tell me where my data and airtime is going? At least if I know its a subscription of some sorts, then i can cancel it. All my apps are closed, but the airtime is still disappearing. Should I port to another service provider or remain faithful to a service provider whom I have been supporting for so many years - but is not delivering the kind of service I used to enjoy?