Hello, are you able to see your contacts when you sign in to Outlook on the web using the same account?
In classic Outlook, go to File, then Account Settings, then Account Settings, select your account and click Change, then choose More Settings, go to the Advanced tab and confirm Cached Exchange Mode is enabled, after that close Outlook and reopen it and allow it time to fully sync, this will force Outlook to download all mailbox data again including your contacts if they still exist in your account.