Dissappearing of airtime

On the 2nd of October I bought R50 airtime. I made two calls which were never answered, but by the end of the day I had a balance of R0.00 . On the 3rd of October I wrote on the facebook complaints page (MTN private complaints South Africa). Until today I haven't heard a thing from MTN and this is definitely not the first time my airtime just disappears. It is really disgusting that I pay my contract every month, but don't get the type of service I expect from our so called "boza network".