Money disappearing

I am on a topup contract and have not had any problem, up until 2 months ago when my 'money' data just absolutely disappeared from my balance.I am always on wifi, if not at home then at work. I do not make calls on my phone, only use whatsup. previously my 'money' would stack up that I occasionally had up to almost R400 available balance, my monthly contract is R178 per month. the past 2 months I have had to top up my phone with more than R100 + per month. All apps on my phone are off, I do not use my phone for internet at all. This morning I loaded R55 onto my phone, did not use my phone at all today except a few whatsup messages RECEIVED nothing sent. When I checked my balance this evening there is R10 missing from my account WHERE IS MY MONEY, I WANT IT BACK, MY HUSBAND AND I ARE BOTH PENSIONERS. I WANT IT ALL BACK AND I WANT IT NOW!!!!!!!!!