Paypal Chargeback

I really need your help. I'm a graphic designer and work in crowd sourcing websites like 99designs, designcrowd etc.

I think most of you know the model of these websites, a client opens design contest and then rate the entries received and then selects a winner.

So there is this website in which I participated ( Don't want to reveal the name as it would be publicity for them ) I never had any problem with this website in past 1 and half years and I have already won more than $2000 from it.

The contest was of Web design and it was a guaranteed contest means selecting a winner is guaranteed.

The contest holder only received 6 entries in which 2 entries were mine. It lasted for 7 days and contest holder only rated my entries and he said he was happy with only my entries. Only I was at top at the end of contest.

But when the time came to select a winner for the contest he didn't select any. But, I was not disappointed with that as the contest was guaranteed
as the policy of website clearly says

If a guaranteed contest is not awarded by the contest holder in 30 days then they would select the winner themselves based on the rating received.

And according to that I was the clear winner after 30days as I received most ratings.

But after 30 days the website said :

No winner will be selected for this contest as they requested a chargeback with Paypal. We apologize for the inconvience this has caused you.


I mean how can they do this ? This is not my problem that contest holder requested a charge back. Website's policy for contest holders clearly says

Guaranteed Contests are non-refundable. A winner must be selected for guranteed contests.

What do i do on this ? How do I report a scam or fraud against the website ?

Thanks