IRS never received my payment but they haven't caught it yet or notified me. How do I pay to avoid penalty and interest?

[Philodog]

I mailed checks to both IRS and my state for estimated tax payments in April 2019. Oregon sent me a notice that I owed 8k  (the amount of the estimated payment) plus 800 interest and penalty. When I checked my bank records neither check was shown as cashed so I'm assuming there were lost somewhere and the IRS is going to catch it sometime. How do I pay them ASAP to avoid penalties and more interest?

[Critter-3]

Pay online :  https://www.irs.gov/payments

[SteamTrain]

And here's the Oregon EFT website if you haven't sent a new check to them already:

(Far right-side window..<<Revenue Online<<<Payments  )

https://www.oregon.gov/dor/Pages/index.aspx

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You should also double-check what addresses you mailed the Oregon and IRS payments to, just to see where they may have ended up...(but if you are paying now, use the Online Electronic funds transfer system noted in the posts above):

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Federal extensions & payments should have gone to one of the addresses for mailed-in Extensions+Payment that are listed on page 4 of the following:    https://www.irs.gov/pub/irs-pdf/f4868.pdf

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Oregon Extension payments should have been sent to the address on page 2 of:

https://www.oregon.gov/dor/forms/FormsPubs/publication-or-40-ext_101-165.pdf

[SteamTrain]

Of course, one of the possible questions we might have...is did you send in 2019 tax "Extension" payments for 2019 taxes?  .....or did you send in "Estimated" 2020 tax payments with 2020 Estimated tax vouchers?  ....those are different things as one is for your 2019 taxes, and the second is for expected 2020 taxes....different tax years entirely.

Of course, the checks should have been cashed long before now in either case....unless you forgot to sign them.......though a lot of paper submissions and filings may have just piled up with no one to process them due to COVID-19.