I received an offer from Avianca to upgrade to business class. I called Avianca prior to making my offer to find out what class the ticket would book under. She told me it would be booked under "D". Since the booking code "D" credits me 125% miles with Asiana Airlines, I made an offer and they accepted it 3 days before my flight. After 4 weeks, I didn't get any miles credited to my account, so I attempted to file a missing mileage claim and noticed that my boarding pass had it booked under the code "I". That code doesn't earn any miles with Asiana. I should have checked my boarding pass before boarding my flight. I've had a few bad experiences with Avianca in the past, but continued to use them due to their favorable flight schedule. However, after this incident and won't be flying with them anymore.