Providing you bought Pro from the official site (www.limewire.com) for $18.88, less than 6 months ago, the thread below has links to help. You should probably send a PM to RSterne & she should be able to sort it out for you
http://www.gnutellaforums.com/showth...threadid=54008

If you were buying Pro from a scam site, there's no way that anyone from LW can help you with payment problems!