Don't panic too much once you are experiencing the data loss. The first thing to do is stop using your phone to avoid possible contact overwritten. Also, you can figure out whether there are backups in iTunes or iCloud you can apply to restore contacts from. To professional recover, an
iPhone data recovery [joyoshare.com] is a nice choice to try. It scans data from iPhone 11/11 Pro/11 Pro Max or even the later devices without backup. Importantly, you can freely preview contacts in real-time to select items efficiently.
How to Recover Deleted Contacts on iPhone 11/11 Pro (Max) [joyoshare.com]