I just got an email from NetFirms letting me know my account was up for renewal. I responded saying that I canceled my Netfirms account back in April of this year, over six months ago.
Then I just received another email from them alleging that my account was not properly closed, and that they only process account cancellations over the phone. I responded quickly, as well as forwarded them the email I sent in April of 2007.
Looks like other people have had similar and worse issues:
UPDATE December 12, 2007: With a little bit of polite persistence, I was able to cancel my NetFirms account without having to call them. They requested I either send my account information (maybe they should add some options on their control panel to cancel?) or email them the welcome email they sent me when I opened the account. Luckily I still had it, so I emailed that to them.