Google Mail is The Problem
Google's email system is quite likely the culprit. I have had a gmail account ever since Google opened their system up to us in the UK. Over the past two years or so I began receiving emails from various place, most notably the US and Canada, that had similar addresses to mine, with dots in different places, or no dots at all. Apparently Google's mail system strips out any "fillers" such as dots, dashes and underscores.
My address format is firstname.lastname@example.org but I regularly receive emails addressed to email@example.com, firstname.lastname@example.org as well as email@example.com. I have tried tackling Google about this but their response is "it can't happen", despite my providing proof that it does. I have had a raft of site registration confirmations as well as more personal communications; even repeated FaceBook password reset requests.
So my guess is that if you are using a gmail or googlemail account then there is the distinct likelihood that your address is being repeated in a slightly different format, or the supposed recipients (if they have gmail addresses) are having your emails redirected to someone else.