You may have missed entering a decimal point or entered it in the wrong spot.  Like in your withholding or estimated payments.  Check 1040 lines 16&17.

Thanks. Checked all figures. Only comas. All looks correct to included estimated payments of $1,000 X 4. All done via Turbo. Line 20a refund is exactly 1,784. Never had this happen before.  Wonder who to call now?  Any suggestion.

Maybe they didn't get one of your estimated payments.  Double check your bank records.

Did you elect to have $1,000 applied towards 2019 estimated taxes?

No sure on how long to wait for explanation.  Do you happen to have good number to call?  Many thanks.