The IRS is backlogged with recording certain tax payments and processing paper return filings due to coronavirus procedural changes at their nationwide mail receipt and processing centers.
My best advice is to respond quickly when and inaccurate IRS notice is received. It may take a few phone calls and long on-hold wait times. However, the time spent straightening out and correcting an incorrect IRS notice will be well worth it so any related additional headaches are minimized.
Take a look at the article here: https://nypost.com/2021/04/07/what-to-do-if-the-irs-threatens-you-over-taxes-already-paid/
