Data usage *****

For the last three months my bill with Vodacom has been three times it usual amount. I queried this with Vodacom as the data portion of my account had gone from around R10 a month to over R1000 a month,I requested itemised billing which showed that data is being used at times when I am asleep ( from 10pm through the night until 6am), I then contacted Vodacom again to try and get to the bottom of it. I found from the bill that The IMEI number that is using the data is not that of my phone Vodacom told me someone myst have hacked my data but that there is nothing I can do about it. I was then told that Vodacom has to protect the identity of the phone (IMEI number that I have on my bill) that is using my data and they would not give me the telephone number or details as they have to protect the person whose phone it is identity. I then asked for this to be escalated to a ***** department and was promised it would be by the call centre. This was over 2 weeks ago and I haven't had any contact from Vodacom to follow up. I now have no option but to cancel my contract and pay an exorbitant cancellation fee as I can't afford to keep paying excessive bills for data I am not using.