In most states there is a law on the books that states that a product must be suitable for the purpose for which it was intended. Moldy feed is not suitable. If this happens again stand your ground and insist they make it right. I once bought an electric dehorner that gave me a shock the first time I tried to use it. I took it back and the little sweetie behind the desk insisted it was my responsibility to return it to the manufacturer for repairs. I told her, no, it was her responsibility to give me a new one. I talked to the manager and much to her chagrin, I walked out with a new dehorner.
yeah I just never darkened their door ever again I think I got my point across to them