Mailed returns piled up in trailers at the IRS for several months during the pandemic. The IRS has recently begun to open over 11 million pieces of mail that accumulated over the time that they were not working on mailed returns. Yours could be anywhere in that pile. You say it was a 2016 return? Nothing is ever going to show up on the IRS refund site about a 2016 refund. The refund site only shows information about 2019 refunds. You say you know that it was received. All you can do then is wait patiently and eventually the IRS will dig your 2016 return out and process it.
Per the IRS website IRS Operations During COVID-19: Mission-critical functions continue:
IRS operational status and alternatives
Processing Delays for Paper Tax Returns: Taxpayers should file electronically through their tax preparer, tax software provider, or IRS Free File.
We’re experiencing delays in processing paper tax returns due to limited staffing. If you already filed a paper return, we will process it in the order we received it.
Do not file a second tax return or contact the IRS about the status of your return.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
