We booked Comfort class on Aeroflot JFK to Moscow and back, the return plane had changed, no comfort class. They gave us $30 each, entitled to more?

Our original booking was JFK to Moscow comfort class connecting to Budapest on a plane that had only economy. We returned from Bucharest to Moscow, economy (comfort not available) and Moscow to JFK comfort class. The evening before the return flight we could not get a boarding pass due to "an error in our ticket, see an agent at he airport" The error was the plane had changed. We had no choice but to come back economy. I have severe Sciatica and it is uncomfortable to fly over nine hours in a cramped seat. They agreed to give my wife and I half the difference between economy and coach. However they only credited our credit card for $30 each. We booked our flight in July 2016 our flights were May 2017. WE booked form our summer home in New York State and paid with a credit card with our permanent residence in Florida as the billing address.