How to delete a datafile if the father-tablespace does not exists? I just know Oracle basic and I would like to know about the datafiles.
I have some files ".dbf" associated with Tablespace that already were deleted. I don't know how I can drop that datafiles and have some free space in my server.

Look:
This is my dbf :
 

And this is the father-tablespace:
select tablespace_name from dba_data_files where file_name = '/u01/app/oracle/oradata/orcl/BGBA_GAL126344.dbf';

Result: 



If I try to drop that tablespace, It says that the tablespace does not exists.



How can I drop that datafile if the father-tablespace does not exists?
The TS associated with your file is 'BGBA_GAL126344', but you are issuing your DROP TABLESPACE on 'GAL126344'.

'BGBA_GAL126344' != 'GAL126344'

Why were you trying to DROP USER?  Neither files nor tablespaces are owned by users.

Why do you repeatedly issue the same failed DROP TABLESPACE command?

FWIW, in 20+ years of working as an Oracle DBA, I have never heard the term 'father-tablespace'.  I think the more correct term would be a file's 'associated tablespace'.