Rapid data depletion

I have a 2 Gig mobile data contract with VodaCotch and over the past six months have had occasions where I'm told I've used up all the data - sometimes within days of the monthly renewal! I've never received a satisfactory explanation - the most common being that my children or work colleagues are using the modem without my knowledge! The problem seemed to have gone away after my last complaint about 4 months ago, but has reoccurred this month when on the 16th I received a message saying I've run out of data. Interestingly, every time it happens I receive sms notifications informing me of their top up options days before the data runs out. When I queried this time, some *********** on the help desk's 1st defence was to say it's because I have a 4G modem, which processes data much faster! So do we have to go back to dial-up then? Something is fishy here and it smells of unauthorised re-allocation of data and VodaCotch can't, or won't intervene. The reason I'm posting this is I've heard from other people that this 'inexplicable' data loss is not unusual. Vodacom is clearly not interested. For consumer press interest, please post if u know of anyone with rapid data depletion problems