DELETE statement not working
Instead of using double-quotes, try using single-quotes:

DELETE 
FROM LOGIN 
WHERE login = '336959686@login.com';


If the delete statement produces no error but doesn't appear to delete the row affected, that means one of the following:


The criteria (the WHERE clause) is not matching the desired row.  
You have a transaction that is rolling back the delete, or has not yet committed the delete.  Check the transaction chaining mode using SELECT @@tranchained;  Perhaps try this:

SELECT *
FROM LOGIN 
WHERE login = '336959686@login.com';
BEGIN TRANSACTION
DELETE 
FROM LOGIN 
WHERE login = '336959686@login.com';
COMMIT TRANSACTION
SELECT *
FROM LOGIN 
WHERE login = '336959686@login.com';

Undetected database corruption - this is extremely rare.  Have you performed DBCC CHECKDB lately?  Make certain you have a reliable backup. Test the backup by restoring it onto another instance of Sybase ASE.  If you have done that, running DBCC CHECKDB should be performed. It may heavily impact I/O, so I would run it during non-peak hours.