You must know that in any contest, for example the Bitcoin price prediction contest, there are contest rules that need to be read and understood by people who want to join as participants.

If you did not read or did not understand rules, but still joined it and broke the contest rules, it's enough for contest manager to disqualify your participation submission. It's valid rights from a contest manager and also the company behind that contest to disqualify you.

You only can complain if the rules don't say that prohibition against participants like you but when you win a contest, the manager pulls some hidden cards to disqualify you. I didn't check that contest but very basically and commonly, there are rules against newbies for reducing abusement and cheat in any contest. I guess it is the same for this contest, then I believe the manager did not do anything wrong with you.