I would explain to him that you think it's best that you don't have a friendship with him and that you'd like to move on completely. And that means no contact.
If he starts asking for the whys, just repeat yourself over and over using the exact same words as above. You don't owe him any more explanations. It is not your fault that the "closure" didn't close things for him.
If he still doesn't get the hint, can you block his number somehow?
When I had an ex like this, I changed my ex's name on my phone to "DO NOT ANSWER", and if he left messages for me, I'd delete them before even listening. After a while he gave up.
Last edited by starbuck; 27-01-10 at 08:18 PM.
“Inside every cynical person, there is a disappointed idealist”--George Carlin