MTN the worst service provider

Good day. What is going with MTN South Africa ?. I have two numbers with MTN and whenever I load airtime it just disappears and when I call MTN to find out what's going on they are telling me that I made calls. Just last night I had R90 on my account and when I tried to make a call this morning it says I have insufficient airtime but how is this possible because i had R90 last night and didn't make any calls. This has been going on for quite some time now and I am tired. I just want my airtime back