Sadly, it's trivial for a spammer to forge your address. It's not your Web host's fault.
Some badly configured email servers auto-reply to spam. That's what you're seeing.
If you want to complain to anyone, complain to the people running the servers who are auto-replying to you. Here's a template complaint I've used before...
Hello. You are sending spam to me by bouncing spam to an unrelated person. I did not send the spam to your server: spammers forge the message sender. Hence, your reply goes to an innocent third party.More info at an old post of mine: I Got 25,000 Spam Messages in Two Days!
Perhaps you sent an unsolicited bounce because your mail server is incorrectly configured. Please don't do that. You should *reject* during the SMTP conversation, not *bounce* after accepting the spam message. It is not necessary for your MTA to send a non-delivery DSN -- you should reject at the point of SMTP RCPT with a 553 error or equivalent.
Or perhaps you're auto-replying to spam. Presumably you filter spam before delivering inbound email. In which case, this reply shows that spam is getting through those filters.
It's bad practice to accept a message for a non-existent user. If you accept and then bounce, you're sending spam. For more information, please see http://www.spamcop.net/fom-serve/cache/329.html
If this was an isolated error, there's no need to be concerned that you will be blacklisted as a spam source. It usually takes several complaints to illustrate a pattern of email abuse.
However, I urge you to correctly configure your mail servers.