If you open the DB with a reset logs... It is a Very good idea to immediately backup.

Any backups taken prior to the reset logs would not be of any benefit in a future media recovery.

It sounds like you have restored a Datafile from a backup taken before a resetlogs.
Don't do that! Its not possible to restore this datafile since the scn information is now mismatched from the log data. There is no way nowto recovery your deleted data file.