2021 Tax Return with $4,440 Refund Showing Code 810 Freeze Since March 2023 - No Movement Despite August Processing Date

I filed my 2021 taxes and I'm still waiting on my refund. The Where's My Refund tool just shows 'still processing' and I've been checking transcripts weekly with no movement. I finally got access to my transcript today and I'm trying to understand what's going on. According to my transcript, my ACCOUNT BALANCE is -$5,440.00 with ACCRUED INTEREST of $0.00 and ACCRUED PENALTY of $0.00 AS OF: Aug. 22, 2023. My ACCOUNT BALANCE PLUS ACCRUALS is -$5,440.00. The information from my return shows: EXEMPTIONS: 02 FILING STATUS: Head of Household ADJUSTED GROSS INCOME: $25,912.00 TAXABLE INCOME: $6,512.00 TAX PER RETURN: $0.00 SE TAXABLE INCOME TAXPAYER: $0.00 SE TAXABLE INCOME SPOUSE: $0.00 TOTAL SELF EMPLOYMENT TAX: $0.00 My RETURN DUE DATE OR RETURN RECEIVED DATE is Apr. 15, 2023, and the PROCESSING DATE is Aug. 21, 2023. The transactions section shows: CODE 150 Tax return filed 20233105 08-21-2023 $0.00 76211-419-94215-3 CODE 810 Refund freeze 03-09-2023 $0.00 CODE 971 Amended tax return or claim 04-15-2023 $0.00 forwarded for processing CODE 977 Amended return filed 04-15-2023 $0.00 43277-518-06155-3 CODE 766 Credit to your account 04-16-2023 -$2,557.00 CODE 768 Earned income credit 04-16-2023 -$3,883.00 CODE 971 Notice issued 08-21-2023 $0.00 I'm really concerned about that "Refund freeze" code 810 from back in March. And there's a "Notice issued" on Aug 21, but I haven't received anything in the mail. I keep calling the IRS but just get the automated message that they're too busy. Has anyone dealt with a refund freeze before? What does it mean that my amended return was forwarded for processing back in April but there's been no movement since then? I'm really counting on this refund money. The transcript shows I should be getting around $6,440 between my credit and EIC, but it's been months with no payment.