Do you have a magnifying glass? Inspect it up close and see if the "fuzz" has legs and is moving. If so, it's not mold. It's grain mites. They're harmless, but they do indicate the feed is probably older than you want. Examine the expiration date on the feed sack if there is one. It may have been sitting on the shelf far too long.
Take aart's advice and demand a refund or a fresher bag. I never, ever toss sales receipts, keeping them religiously in a large envelope for just such developments.