Data bill 35 times as large as my normal bill!

Last night before I went to sleep, I still had basically all of my data left, as I use very little of it. At home, my phone is permanently switched on Wifi which runs through CellC. My mobile data is thus almost never used. This morning when I woke up, I suddenly had a bill of R3500. This is physically impossible. Clearly, some kind of error happened from your side, because all my automatic updates are disabled, and I was sleeping while this absurd data bill accumulated. Further, when I got this contract from you, I called you to set up a lock on my account so that it would never exceed the R99 (now R109) contract that I signed up for. This has to be addressed immediately.