Money disappearing from my mom's phone

I am writing this on behalf of my 83 year old mom who is hearing impaired and is unable to phone to make the complaint as she cannot hear well. We had noticed that her data is being taken, every day, exactly R5! This has been going on for some time and she has probably lost well over R200 by now. She was in our Wi-Fi area all holiday and even when she had made no calls, sent no messages or even been away from our home, the R5 was taken. We would appreciate some feedback regarding this matter please, or I will have no option to use social media to complain. I have been taking photos for proof of this happening.

The above letter I wrote on the Vodacom complaints website 2 weeks ago and have had absolutely no contact from the company, it is as if they just don't care that the money is disappearing from my mom's account, the worst of it is that she is a pensioner!!