I sent in a payment via USPS Priority mail with a signature verification upon receipt required for 2019 taxes owed on a trust.  They sent me a notice saying they did not receive payment...they lost the check.  I tried calling and was on hold for 2 hours and then the call was dropped.  I stopped payment on the first check and sent a new check which was signed as received be them on August 24th 2020...it's September 16th and the check has not been cashed.  I also had to send in paperwork and proof that I sent the first payment in.  All I have is proof that I sent something and they signed for it...there's no way to prove I actually put a check in the envelope.  The IRS is trying to access a penalty for late payment so time will tell if they accept my proof and waive that penalty.  I sure would feel better if they cashed the second check!