Problem with 1099-NEC & Amended Return

When I originally filed my 2020 taxes, I had originally reported $27,126.25 in 1099-NEC income. Subsequently the bookkeeper sent me a corrected form showing $21,426.25.  I then filed an amended return that corrected to 1099-NEC amount & explained in Part III that bookkeeper sent me an eroneous form.  When I completed the amended return, it showed I had overpaid by $804 and I expected to received that amount back from the IRS.  It took them over a year to process and I've been on the phone with them twice as they say the file is closed and they owe me nothing. How could that possibly be when my business income went down $5700.00?