Remember that before we go straight to blaming the company and yes they may be at fault here, that it is also likely that the mouse got in during storage and transit or even in the store. A mouse can get in a amazingly small hole, so small it's shocking really.
Anywhere you have large food storage there is some amount of mouse activity, I personally pour my cats food out of a bag into a sealable tub before using it to keep mine safe, I suppose it has the secondary effect of letting me look at it before I start using it. It was not the original reason I do it, freashness is, but now I'm very glad I do.
So yes let's keep this to PM's if you feel like sharing the info. And possible better yet, understand that as gross as this is it can happen to any bag of food from anyone.