Short of contacting the agency again, taxpayers always have the ability to make an estimated tax payment.
I don't really like recommending estimated tax payments because they are date sensitive with respect to any potential interest and penalties on a tax return. It is therefore better to make your estimated tax payment through additional withholding which is counted as having been paid in equally throughout the year.
In a case where one is avoiding tax through the use of withholding late in the year, this might be a bad response, but in your case, you are trying to have tax withheld and you are doing your part, so definitely go the withholding route.
You can have withholding taken out of SS or perhaps also your pension payments.
If you make an estimated tax payment now, you probably wouldn't be subject to penalties either, but that is based on personal circumstances, so see this form to make an estimated tax payment (forms at back of book):
Let me know if there is anything more I can do to clarify for you.
Thank you for your question.