You say you were one of the last to board, when did you board? Was your BP printed out at least 15 minutes prior? Were you int he gate area at least 15 minutes prior?
If this is the case and you used your miles, this means you paid for the class of service. Call again, write an email again, call the Post Flight Resolution at Customer Care. They can't just do that on whim if it was not a comp upgrade. Your status should not matter here