if e filed, was it accepted? if yes, there should be postmark report. write back to IRS that it was filed timely and enclosed a copy of postmark report.
if mailed, did you keep receipt. do same as above as far as responding to IRS except enclose copy of postage receipt.
if you don't have receipt and if you have always timely filed in the past, write back and request abatement. your letter should include
statement that prior returns have always been timely filed
and that you have taken steps to insure timely filing in future
and that you are requesting abatement of late filing payment
