Just to get a lawyer to write them a letter, offering to replace the aid at their wholesale price, might cost $200 - $500. If you bought one somewhere else and gave it to them, could they refuse it, if it is the exact same model and in an unopened box? You could ask them if they would accept that. If they don’t, and they know it is exactly the same aid, then they are not acting in good faith.
But if they will accept one bought somewhere else and in a new unopened box then you might PM some of the pros on the board and see if one will order it for you, for a reasonable charge.
Another option might be a local TV station “on your side” thing where they tell both sides and how they worked it out.