Urealistic Data Consumption

I have taken a contract for data some time last year 2017 around may, ever since I took the contract my 10Gig data will be finished before the 10th of every month, until recently I called to enquire about the issue first they told me that it shows from their side that am connecting to internet, recently it was finished by the 8th of January I called and they told me that on Sunday I used 4gig data of which I found very unlikely because my router was off for some time during the day and I haven't even downloaded anything. am very disappointed because am nit getting any assistance from Vodacom.