You are not part of the solution. You are part of the problem. “Autoresponders” to spam mails are a bad, BAD idea. Most spam comes from forged senders; an autoresponder will reply to that forged email-address. Usually that leads to a party that had not been part of the spamming and is being abused just the same (commonly known as joe-jobbing). Autoresponders are a crock of ****; if you ever get joe-jobbed, you will know what I mean (happens every couple of weeks here; Spam filters catch most of the crap that arrives, but autoresponders usually get through. Hundreds of them, many claiming that due to too much spam, the account is closed. Sometimes I get dozens of mails from a single account.
You are obviously aware that this is happening, since you know what a joe-job is. As such, this practice is the most selfish thing you could do. Thanks.
(just drop mails like that in the SMTP conversation with a proper error message, not later on as a reply; you can make your error message say whatever you want; legitimate senders and spammers alike will get it, though the latter won’t care (and may even stop sending you crap once they only get SMTP errors from your server)).
To the OP : You are SOL. Once your mail address is in their databases, it’s not gonna get removed, no matter what you do. The problem is gonna get progressively worse as the address keeps getting “passed around” (i.e. sold in lists) between scum. As for how they could have gotten page@ – page is a common English word. That’s probably a simple dictionary attack. Firstname.Lastname only protects you from spam if you never communicate with anybody, ever; all it takes is one infected winblows box for the address to be harvested. For stuff such as paging email addresses, you might want to use a whitelist-approach (though even that will usually not save you from forged senders; you might have to consider signing your mails with gpg and only allowing properly signed messages to go through to your pagers).