microsoft office 2011 for Mac Outlook uses huge amount of bandwidth when open

Had MS Office 2011 for Mac for about a year before this problem started at the end of 2013 (maybe following an OS X 10.9 update or a MS Office update). As soon as I open Outlook it begins running and if I leave it on for a day, it eats about 15-20GB. My Internet provider is threatening to charge me for the extra usage (over 200GB in April 14). Prior to this past several months, my average BW usage was about 4-5GB per month. Yesterday I moved the Outlook folder to the trash. I have an Exchange account and 4 other imap accounts on Outlook. Does anybody have any ideas...I'm dyin' here!