You can request documents from the IRS. You want to request a copy of the bogus 1099 that the IRS received for you. You probably want to check other years as well to make sure this problem doesn't also exist in 2019 or 2021.

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

You can challenge it in both places. If the employer is basically a legit, non-shady employer then ask them why the fuck they sent this 1099. If there is shadiness, it might be a manager stealing from the company (manager says you're still working, pockets your salary himself). Perhaps they reported that they hired you to get PPP cash.

At the same time you can write a letter to the IRS stating the situation and flatly denying doing any work for the company in 2020 or receiving any money from them.