First off, use a join, don't do multiple tables this way. It's such an old style of doing it that I don't even remember what it is called.
Do something like this:
SELECT farmer_code, bank_name,
CASE b.ISFC_Code LIKE '%ALLA%' AND LEN(f.bank_acno) = 11 THEN 'Correct'
ELSE
END AS SomeNewField
FROM farmer_master f
LEFT JOIN bank_master b ON f.bank_code = b.bank_code