As to why you have been blocked indefinitely, the reason is that you have confirmed yourself to be underage.  FANDOM Policies distinctly state that "you confirm that you are 13 or older and acknowledge that the Service is not intended for children under such ages, as applicable." The reasons for this are legally binding and are more for protecting children your age from the dangers of online predators and other malicious activity than to forcibly block you from using these. Your account will be terminated shortly, once I get through to FANDOM.
Any further attempts until you are of age to create accounts will result in them being IP blocked and reported (you will not be able to create any more accounts from your computer.)