Hi Chrisst,
This issue is related to the client. When you have your account on the Mac Mail application, the client will automatically create an address list called Suggested Contacts and it will be updated to OWA. Since you have multiple accounts on the client, it will look through all of the accounts and create contacts under Suggested Contacts and synced to Office 365.
You can click on the link below to post a thread in Apple Mac OS community to get professional support from them to get the issue solved.
https://discussions.apple.com/community/mac_os/mac_os_x_v10.7_lion
Thanks,
Yang Yu