MTN charging pensioner over R2000 a month suddenly

I am really disappointed in the service that MT has provided to my 84 year old grandmother. She has been a loyal customer of yours and has regularly received bills from you which she has diligently paid. Please note that these bills are minimal, and well within the range you could expect a pensioner to pay. HOWEVER: This month she received an extra bill of approximately R2181. This bill was deducted from her account via debit order and has now left her unexpectedly in dire straits financially. Her data number that gave rise to the charges: *** (MTN you are welcome to call me to get all of her details which I won't be posting on an online forum). On our side, we absolutely cannot figure out what this extra cost is for? My grandmother (being 84 like I said), does nothing more than send an email or two a week or - perhaps once or twice a week - she Googles something. There is no valid way that she could have used up over R2000's worth of internet data in a month. We haven't gotten an itemised bill (despite requesting it THREE times) and I am sure that everyday she is being charged MORE and we won't know until the month ends. Awful customer service, cannot get any help AT ALL!