Go to
Google Contacts and see if they're there. If they are, syncing should bring them back.
If not, hit More, then Restore contacts. You can restore contacts that were deleted up to 30 days ago.
(This works only on contacts entered as Google contacts. If you entered them as Device, Phone or SIM contacts, they're gone - which is why
all contacts should be entered as Google contacts - even though, for some reason known only to Google, that's not the default, and if you don't change it, the contact you're adding becomes a Device contact.)