Hi!  Yes - my client is in the same situation.  She made payment on a trust for 2019 back in July.  In September she received a notice that the tax had not been paid and was issued another bill including interest and penalties.  Believing she had overlooked the initial payment, she mailed a replacement check.  Ultimately, the initial check was cashed by the IRS in early October and the replacement was cashed by IRS in mid-November.  So now both checks have been cashed by the IRS and my client is out the second amount at this point.

Does anyone have any ideas / suggestions on where to go from here to get the second payment refunded?

Many thanks!