Disappearing Airtime, useless call centre

i have been having a problem with my airtime disappearing, its been months now, but everytime i called i got told the "your apps are using up your airtime" story, i stopped calling and tried to manage this problem myself, now i can only load airtime in bits and pieces to avoid it just disappearing with no explaination, monday R55 was loaded for me, i used some of it to buy data to use for whatsapp which is the only app i had open on my phone , all the other app i use on my work pc, so i always make sure they off and they were off, my R28 disappeared 5minutes into whatsapp as confirmed by the agent, but as far as i know whatsapp cannot and has never used R28 in 5minutes esp when i had data, so since i had all my applications off , no one can explain to me what happened to my money, iv let this disappearing airtime situation go for months cos i knew i wont get any assistance calling in, now R28 is a lot of money, i need this sorted out, call centre is so useless, i was on a call with someone for 30minutes, who kept putting me on hold and giving me information thats invalid to my call, the prev agent "logged a call" and promised a call back which ddnt happen, ive been with vodacom for too long but i cant keep spending money on airtime that just disappears.