Letter from the IRS 2

I am self employed and filed last March expecting a significant refund. I've yet to receive it. In looking at my return I appear to have paid the full self employment tax although there is an item in Schedule C line 12e as you described above. In August I got a form letter from the IRS (letter3064c) telling me about the employer's share of Social Security tax due, zero for 12/31/21 and $503.88 DUE 13/31/22. It also states I reported a deferral of $503.88 on Schedule H of my return. There is no Schedule H on my return.

I've tried multiple times and avenues to contact the IRS but without success. HELP!