I'm assuming when you say Outlook, you're referring to Outlook.com?
First question I will ask is how many Outlook emails do you have on your devices? It's possible the duplicates are coming in from that. You can filter your contacts in People on your devices. I'm not familiar with the Surface but on WP you simply go to People -> ... -> Settings -> Filter my contacts list
This should help you reduce your contacts.
If you log in to Outlook.com you can use the People tab there to manage your contacts.