Data goes missing

My cell c modem uses an excesive amount of data since monday,,after reporting this to cell c, we were told by their technical dept that this is because of a laptop setting that causes outlook to update automatically,,yet, when using a vodacom modem this does not hapoen,,,doesn't the same settings apply,,contacted them again yesterday and was promised that someone will call me and assist,,,still waiting and the modem is still taking data, EVEN WHILE BEING UNPLUGGRD AND OFFLINE ????