MTN TOOK MY AIRTIME

I had R34 airtime. When I checked my airtime it was R00 I called MTN they tell me check again because on their system it showing I have R34. When I checked again I had R11 I called again they told me i had open 3 applications running on my background. I asked what applications because I am using only whatsapp I haven't used even Google. They said they don't know which are those applications oppened. My airtime was gone just like that.