notice u/s 143(1)(a) for demand

What was the reason for disallowance........ Whether return filed after due date or turnover exceeded tax audit limits?

Check the reason first and if everything as per order, reply accordingly.

no turnover was under the limit and return filed under due date
we are raising rectification return but it is not been raised

intimation under section 143(1) can be issued within 1 year from the end of financial year in which return is furnished. Assuming you furnished your return within time limit prescribed under section 139, intimation can't be issued now. However this could be a case of income escaping assessment(147). For that also notice(148) could not be issued after expiry of 6 years from the end of relevant assessment year in case income alleged to have escaped assessment exceeds 100000. If it is a notice under section 148 and it is issued after 31/03/2018 then it is invalid.However I would recommend you to seek professional advice.

OK Thanks