I've made an e-book and i've sold it on DigitalPoint. 2 days later i receive the following mail: " This is my second request for a refund of my $5 for purchasing your ebook. Your ebook is teaching methods which are illegal through the use of pirated software (Hummingbird). Please refund my purchase price immediately or I shall take the matter up with Paypal directly and file a complaint with http://digitalpoint.com/ Thank you." What should i do ?