Complaint mtn

I have a contract with mtn for wifi. We do not use the day time data often and yesterday I used it for 20 min today it says the data is o.oo how is this possible. I would like an enquiry into it as what is taking all the data I do not understand this at all it is impossible. I have tried to email and phone mtn account department and am not able to get anyone to assist me when i do get threw to someone they say they offline or keep transferring me. I have a daughter in matric and 1 in gd 10 that use it to study and now cannot use it as I am being ******. I got this contract to assist the kids with schooling and they cannot even use it daily as the data just disappears. Mtn has rep**** to my complaint saying it was used for internet but how ?? In 20 minutes it's all gone