You need to go back to the airline. If nothing else they need to know one of their employees / agents is seriously misinformed on the visa requirements. If they are not the airline who charged you the change fee you need to ask them to either refund you the money themselves, or get the issuing airline to refund you. Don't forget to ask for compensation for wasting your time, etc.
Be as clear as possible as what you want from them. That actually makes it easier to deal with your claim.