passcode is not working

The passcode and FaceID didn’t change themselves.

Perhaps “someone else” has passcode and/or FaceID access to your device … ??? 🤔

Regardless …

If you can’t determine the current passcode, your ONLY option is to reset the device and restore from a backup.

If you see an iPhone or iPad unavailable message or Security Lockout screen – Apple Support (AU)

Going forward, suggest consider changing your device Passcode AND AppleID password AND resetting your FaceID.

Also, review your AppleID at https://appleid.apple.com/ to verify that there are no “unknown” Devices or Trusted Numbers listed.

Lastly, see:

If you think your Apple ID has been compromised - Apple Support

BTW, did you try a full power-off and restart ?

I hear ya’ about not changing it … but unfortunately, if the power-off restart doesn’t resolve it, nothing will change your way ahead.

The device gets the “final say-so.”

Restart your iPhone - Apple Support

And if necessary …

Force restart iPhone – Apple Support (AU)

BTW, did you try a full power-off and restart ?

I hear ya’ about not changing it … but unfortunately, if the power-off restart doesn’t resolve it, nothing will change your way ahead.

The device gets the “final say-so.”