Your reply should be based on the facts of your case.
Are you liable to deduct TDS? If yes, then better apply for TAN and deduct TDS in future. Anyways, with regards to earlier payments, the AO would anyways disallow expenses where TDs was deductible but was not deducted.
So first establish the facts of your case and then accordingly you can reply. Ignorance of Law is not going to be a defense here.