Demand u/s 143 intimation time barred

kindly make it a healthy discussion.

The issue is in audit report the auditor reported non deduction of TDS on rent paid.  AO added back the income and issued demand under section 143(1) a.  But the assessee had obtained form 26A from the landlord.  Auditor has not attached the form 26A with audit report.  Assessee is a partnership firm.  What is the remedy now available?