Go on their website and call their 800 number. Speaking to someone is actually better than an email, I've worked in customer service for years and know this for a fact.
A few years ago I found foil pieces in a box of mac and cheese, not from Kroger. I'd been planning on serving it to my children so was understandably miffed. I called the 800 number and within an hour someone who specifically handled complaints called me back and asked if she could come out to take a report and pick up the box. She explained that they take these type of things very seriously and needed to know where it was manufactured, etc..
About 10 days passed after she came out and I received a call from her telling me they'd investigated the plant it came from and could not figure out how the foil got into the package. She also told me she was putting a letter to that effect in the mail to me and sending some coupons. OMGosh, I received oodles of coupons for free items, and when I went to the store and used them all at one time the woman behind me almost fainted when she saw my total go to zero!
Last year I had a problem with a bag of Up & Up diapers from Target, the tapes ripped off 3 of the diapers in the package when I went to fasten them. I called, they asked for the codes on the bag, where and when I purchased them, and sent me three $3 coupons that more than covered the price of the diapers.
And a friend of mine bought a 6-pack of Pepsi, and when they got home they found that one of the cans, though sealed, was completely empty. Pepsi sent them cases of soda when they complained.
Companies really want to hear when you have a problem with their products, so follow through with a call, tell them you emailed them but wanted to make sure they didn't overlook it, and be pleasant. Trust me, that will go a long way in them wanting to keep you happy!