MISSING AIRTIME

I loaded airtime of R275 and my balance was then about R308 on the 20th August 2015 afternoon. When I got home and wanted to convert my airtime to data to my surprise my balance was now about R189,so that means about R119 of airtime had just disappeared. In the evening I called the call centre to inquire about my missing airtime and the first agent told me that there were applications that updated yet my phone would prompt me to agree to the updating of the applications and I didn't see nor receive notification once those updates finished. Why is it that the updates also didn't happen when i had data and update using my airtime,he couldn't give me a straight answer. The second agent gave me attitude and told me it was internet usage yet I know that was not the case. She didn't even try to offer any solutions and was back chatting instead of listening to what I was saying. So since there are conflicting views to my airtime that disappeared which reason am I suppose to take?