CellC reap off my wifi data

I have never been this shocked in my life. 2 weeks I app**** for a 10gb wifi router contract with Cell C. The service rendered was applauding and I got the router delivered to my work address on the 30th of June. On Sunday the 5th I couldn't access my phone I check the wifi connection and it says no internet connection. I then contacted Cellc spoke to an agent who advised that my 10gb day data is depleted. I was so shocked never have I used not even 2gb in one week as for 10gb being depleted in 5 days, she then gave an option to increase my limit with 2gb for R199 which I agreed to because I wanted to connect on internet for something urgent and that did not even last for 30 minutes. So basically 12gb is gone just like that in 5 days, I am really upset and disappointed with Cellc I have used this network for more than 15 years and never ever had I used 12gb not even monthly, They lady logged a call with the IT Department on Sunday to say they will revert back to me kn Monday which they didn't, I really need an explanation and a detailed statement as to where did the 12gb disappeared to before escalating the matter further.