Bad service

I have a WiFi contract and for the past 3 months my data has been depleted mysteriously. This month I did a test, I checked my balance before using my device and data for the month. I was surprised whn they said Ive already used 7gb whn I haven't even used the data. I've logged a complaint last month, no response since they ( Londiwe Sokhela) said I should send my account details and yet my data keeps getting depleted.