@OP: I'm not sure what happened. That does sound weird. You might have gotten the post-block message because your block request needed a little time to be processed.
If you keep getting the messages, you can report the member to the staff via a Support Ticket. However, I suspect that if the member continues to send messages as frequently as you have described, the member will soon be banned for spamming.
You were invited but didn't decline
http://www.chess.com/tournaments/players?id=48772&sortby=alphabetical&page=3
The messages you're seeing are updates (tournament announcements) posted by the TD wallyjack on the top of the tournament page.
Ah I managed to dig up the initial invite and clicked decline. Should be fixed now. Thanks!
Btw, just a suggestion, since those additional messages are 'updates', I think it would be helpful to include an option to decline/opt out at the bottom of those as well (in addition to the one shown on the initial invite) to make the option more accessible.
I received several messages from someone about a tournament on this site. I had no intention to join it but I got message after message with updates on the number of people signed up for the tournament. After receiving some messages I sent a message back to that person asking to opt out of the invites (I'm assuming he sent out a load of invites via mass messaging but I have no idea how he got hold of my username). I also put him on my 'block' list. However I then got yet another message despite the block, and when I tried to send yet another message I found I couldn't send it cause he blocked me! This does not make sense, I blocked him and he can continue to spam me, and yet he's blocked me and I can't message him? What's going on here?