"I filed 5500-EZ Delinquent Filer Penalty Relief Program along with $1,500 check for 6 years of returns in December 2020. Solo 401k. IRS cashed the check but later sent me a letter asking me to pay. I replied that I already paid, that was in March 2021 with me sending proof of the cashed check. I got another letter in September, two weeks ago, saying the IRS has a $1,500 check from me and needs to associate that with a return. I faxed a reply saying that's for my 5500-EZ. I called the IRS number and the rep is saying that the $1,500 was applied to certain years like 2016 but not to other years. So 2014 and 2015 don't have a payment on file. 2016 does. The 2017, 2018 and 2019 returns have not been processed yet. I sent in these forms last December.

Now I got a CP 283, demanding I pay $300,000 within 30 days!

I called the IRS number and the rep told me to fax documents, responding to the CP 283. [1] Should I contact the taxpayer advocate? [2] What happens at end of October when the CP 283? Any help is greatly appreciated as I am in a state of panic."