Okay, So you have right-clicked on them, click delete, then check the box that says "I also want to block this contact" press okay, you have blocked and deleted the contact, if you delete the contact without blocking they can still talk to you, they just won't be on your contact list, so make sure you block them. When they delete you you can remove them from your block/delete list so then you cannot re-add him. Hope this helps, Brett.