OnePlus
Import Contacts from SIM or VCF File auf OnePlus
Contacts on a SIM card or inside a .vcf file are not automatically linked to the Contacts app on a OnePlus phone. The app only reads data that has been explicitly imported, so numbers from an old SIM or a backup file stay hidden from calls, messages, and search until that step happens.
The import runs through the Contacts app itself: Contacts ➔ Menu ➔ Settings ➔ Import. From there you choose Import contacts from .vcf file or SIM 1 / 2 and confirm with OK.
The next screen decides where the contacts end up: Save imported contacts to Google account or Device. Saving to a Google account keeps the contacts synced across future phones and survives a reset. Saving to the device only keeps them locally, so they disappear if you reset or replace the phone without a separate backup.
If you picked the .vcf option, the system then asks you to Choose a .vcf file from storage. Pick the correct backup file, since choosing the wrong one can import outdated or duplicate entries. Duplicate contacts after import usually mean the source file was merged into an account that already held some of the same numbers.