If you are 100% sure that you bought it from Limewire.com and not some scam site, and you are sure that the payment went through, then PM http://www.gnutellaforums.com/members/limenathan.html

Although it seems as he might be on vacation (Last seen 3 weeks ago)

Alternatively just download either an older Limewire or Phex from my sig, which in my opinion wipes the floor with the newer Limewire.

If you are into Torrents then Azureus (also in my sig) or uTorrent is the way to go. Don't use Limewire for torrents.