@jidong1 - if you feel comfortable doing so, I'd include a copy of the SS card as documentation, since the issue date is printed on it.
you didn't state it, but can I assume you indeed filed prior to 10/15/21?
did you maintain a copy of the extension form? I'd include that as well. Maybe they didn't update your record to document you filed an extension.
Look at your transcript - anything there help your case documenting either the extension occured and / or the date you filed your tax return?
