Korat immigration office has 3 separate offices (1) The big office is for yearly extension of stay.

(2) A smaller office/ building 30-40 meters away from the big office, the notice on the door says 90 day reporting.

(3) A small office next door to the 90 day reporting for notifying the address where you stay.

Maybe you went in the wrong office

I did my yesterday and got the same, also I have reported every 90 days at Korat.