The below details might help us.
show parameter undo
select * from dba_tablespaces where tablespace_name='UNDOTBS1';
select * from dba_data_files where tablespace_name='UNDOTBS1';
SELECT STATUS,RELATIVE_FNO,TABLESPACE_NAME,COUNT(*) FROM DBA_ROLLBACK_SEGS GROUP BY STATUS,RELATIVE_FNO,TABLESPACE_NAME;