I'm guessing you didn't use a contract?
I would go ahead and sell it, i think over a year is long enough to wait for payment
The only problem is with the design still being on his site. I would leave him one last email and phone message telling him that since payment has not been received, you will be selling the design and contacting his host about displaying copyrighted work.
Then contact his webhost, explain the situation to them and request that the design be removed to avoid you taking further legal action (you don't have to mention you don't really plan on taking further legal action
)
If you really want to go all the way, you could also report his WHOIS information as being false as he has not responded to emails or phone calls), and if the domain gets taken away the design will also disappear off his site