Missing airtime

I think I have kept quiet long enough about Vodacom and this whole airtime going missing story... I had R3.25 airtime last night and I took an advance of R10.00. I then proceeded to check my balance and I had R13.25. So I bought the my 5 bundle which is R6.00. And that left me with a balance of R7.25. But low and behold I have only R0.19 on my airtime balance. How is that if I did not even use the airtime last night after I purchased my . And this is not the first time that this has happened where I load airtime and yes the deduction of the advance goes off which is fine. But later when I chalk my balance the airtime has just vanished and considering that I hardly use my data because I am on wifi 90% of the time I am completely Un happy . I honestly think it's time I switch to cell c because Vodacom has been nothing but a headache to me. And the next thing they are going to want to call me and give me some lame explanation.. I'm over this really