Here are some instructions to follow to attempt to get the contacts back if you deleted them by accident. 

If you accidentally delete a contact or a contact list in Outlook on the web, you can restore the contact or contact list if it's still in your Deleted folder on the People page. In some cases, you can even recover a contact or contact list after it's removed from the Deleted folder.
Note: To go to the People page, sign in to Outlook on the web and select the People icon People at the bottom of the page.

Restore contacts that are still in your Deleted folder

When you delete a contact or a contact list, it's moved to the Deleted folder.
  1. On the People page, in the left pane, select the Deleted folder.
  2. Select the contact you want to restore, and select Restore.

Recover contacts that have been removed from your Deleted folder

If you can't find a contact in the Deleted folder, the next place to look is the Recoverable folder.
  1. On the People page, in the left pane, select the Deleted folder.
  2. At the top of the list, select Recover deleted.
  3. Select the contacts you want to recover, and select Restore.