Estimated Tax Payment not credited

[carolalto]

My clients made a 4th quarter estimated tax payment for 2020 taxes on January 10, 2021.

They have proof that the check was cashed.

The IRS just sent them a notice that they owe $40,000 for 2020.

Help!  What should we do next?

They do not reply to letters.  I have tried that with another client.

[sjrcpa]

They eventually reply to letters.

If you are the third party designee you can call and 'splain.

[qbteachmt]

"The IRS just sent them a notice that they owe $40,000 for 2020"

How do you know the issue is that one payment? Have them pull their tax account transcript:

https://www.irs.gov/individuals/get-transcript

[BobKamman]

Was the check for $40,000?

Did they mail it with a 1040-ES voucher for 2020?

They eventually respond to letters.  You can call and listen to music for three hours and someone will tell you to mail them a copy of the front and back of the check.  Or you can do that without calling.  

[Just-Lisa-Now-]

Respond to the letter with copies of the canceled check that they arent showing record of receiving.