they deemed you as not a genuine tourist meaning to many visa exempts entries in a short period of time, thus upto discretion of the immigration officer.
You could have just got 60 day visa exempt on arrival and then extended for 30 days at immigration for 1900 as you have said. So embassy is correct you can stay for 90 if you extend that visa for 30 days. I think you may have applied for a multi entry going by the price. Seems like there was some confusion along the way.