MTN the airtime ********

I have now been losing my airtime when I recharge. This morning I charged with eight rand from my bank account. Before I could do anything the airtime balance was on 4rand something. I let it go. Later on I recharged using their extra time service for a R20 recharge. When I tried to purchase bundles it said I was left with R12 something. I called customer service and spoke to Claudia who could not see any thing. She said I should call back after 30 minutes. I called back and Lucia picked up the phone. I explained my predicament to her. She told me that the airtime gets reserved for applications. I tried to explain to her that I shut off the data. She told me that the airtime gets used for applications even though I shut off the data. I warned Lucia that I was going to take action to get the matter resolved, but she couldn't care less. I lost my airtime only to get brushes off when I seek help from MTN