Somebody did this to me, too. I've never bothered to take action about it. Realistically, what harm is this doing your business? Customers who weren't getting to your website anyway aren't getting to your website. A microscopic number of customers, actually, since direct navigation is all but dead these days -- thanks, Google. If you doubt me, pick another off-by-one domain name and typosquat yourself, then read your HTTP logs.

Some people on the Internet are jerks. Oh well, you've got more profitable uses of your time than to worry about them.