Billed wrong

In the beginning of October we tried to use our internet stick . However we could not. We phoned in to find out why not, the explanation was that we owe Auto page R12 000 for using 18GB of data. After a long fight with the consultant , we found that this data was used on 2 July 2015 (Thursday) 2 am. This is clearly a ********** activity seeing we are asleep that time of night due to all of us working the next morning. We tried to explain the situation, but no one wants to listen. We then agreed that fine just to keep our name clean, and off the black listing. we were advised that the only way to pay this is in 3 months , that gives me R4000 a month to pay for something that I did not use. Please assist us in this situation seeing this is truly not us that used this internet.