Contact list

It all depends where your contacts were stored. If locally on the device your only hope is the backup of the device you made it prior to the incident. Luckily for you, when your are signed into iCloud, unless you have deliberately turned that option off, your iPhone/iPad makes backups automatically when the device is connected to power and on WiFi at the same time. You simply would need to restore the backup onto your device.

If missing contacts were synced through iCloud, follow https://support.apple.com/en-us/HT205018 to recover missing contacts.

If missing contacts were synced through non-iCloud over the air account (e.g. Google, Outlook, Yahoo, Exchange, carddav) then you need to contact with whomever provides support for the account to see what recovery options they have to help you recover missing contacts.