Food Gone Off long before expiry

I recently purchased a bag of dry bob martin pellets after switching from hills science plan. I assumed that this would be a better option as it includes moringa. Upon opening the 3rd bag, the pellets were covered with webs and dead insects. It was due to expire for months and was purchased from a reputable retailer. The bag had no tears and openings in which anything couldve crawled in to make these webs so this came packed as if was from the factory. My dog got seriously I'll. I contacted bob martin, after numerous emails back and forth, all I received a was a replacement voucher for a new bag of food. Had my pet passed away due to this negligence, what would a replacement bag of food do? If I wanted, I couldve taken the bag back to the retailer which wouldve been less of a hassle than contacting bob martin. The food as well as the service is extremely disappointing and other buyers should be weary of this.