tax payments with 1041-V.

You are lucky you received signed receipts, as many offices were closed. The dunning letter is probably a computer gone mad with COVID-19. If the checks have been cashed, just ignore the notices. 

This seems to be a common problem this year.

https://www.irs.gov/newsroom/irs-operations-during-covid-19-mission-critical-functions-continue

"Notice Mailings - Some Due Dates Extended to Help Taxpayers: The IRS began mailing backlogged letters and notices to taxpayers in the agency’s steps to return to normal operations. Because of the COVID-19 shutdown, many of the notices were mailed with past due payment or response dates. To save time and costs, the IRS in most cases will not generate a new notice. Instead, the IRS will include Notice 1052, Important! You Have More Time to Make Your Payment, as an insert that will provide a new, updated pay or response date. Please read the insert carefully. It explains why the notice was delayed and, more importantly, provides a new date in which to pay or respond. Below are key points recipients should note when the notice is received. They should:

• Review the last page of the insert to determine if there is a new due date.
• Disregard the notices if steps have already been taken to resolve the issue.
• Visit IRS.gov/coronavirus for more information.
• Contact the IRS using the number on the notice if you have additional questions. Keep in mind that phone lines remain extremely busy as the IRS resumes operations.

Extended Due Dates: The expired payment due dates printed on the notices were extended, as described in the insert. The new payment due date was either July 10, 2020, or July 15, 2020, depending upon the type of tax return and original due date.

More than 20 million notices were mailed since early June with either the appropriate insert or with current dates. Due to an error, affecting a fraction of these notices, about 11,000 notices were sent without the insert. Upon discovery, we immediately began reaching out to these taxpayers providing them with the appropriate information regarding the corrected due dates for a response to the notice and have updated our systems accordingly. All notices that were previously held as a result of the temporary closure of our facilities, have been mailed. As such, this should not be a reoccurring issue."