Can you block a contact? Just deleting them doesn't work as they still have your PIN.

Yes you can.

To block a contact in BlackBerry Messenger, complete the following steps:
[LIST][*]Open BlackBerry Messenger.[*] Highlight the contact.[*] Display the menu.[*] Select Delete Contact.[*] Select the ignore future invites from this user check box.[*] Select Delete.[/LIST]The link with instructions is here.

Ah, thanks. I didn't delete them as I didn't know the ignore option would come up

Thank you.