Prepaid Data Disappears for no reason.

Just had 2 incidents where prepaid Vodacom Sim cards use up 400mb of data within 5 minutes without any devices connected to the router, checked for WASP services and nothing... where would data disappear to at 80mb a minute with no devices connected ? Third sim card no problem. Seeing its prepaid you get no support from Vodacom but they take the money and no responsibilty. Wish I kept the Sim's to give more detail but be warned when using prepaid sim cards.