Feeling ****** by MTN

I have a R100 voice top up contract (NO DATA) I use my wifi data and occassionally buy a data specific bundle, I have roaming set to off and when I leave home, all my services that use data, stop working until I reach home again or load a data specific bundle. On the 2nd march my entire R100 voice package was allowed to be converted and used for data when I left home. At no time did I approve this and it has never happened before. The only answer I got from the call centre was that if my whatsapp connects to the internet when I leave home it will convert my voice to data. This is ridiculous. In my experience one is always prompted to convert voice to data and I definitely did not do this EVER!! I have bought many bundles which have been used up while I have been away from home and NEVER before did my phone just switch over and use my voice bundle to continue. It has always just said... no internet... your data your bundle has been used. I logged a fault but no-one has ever responded. Absolutely pathetic.