As above: You need to contact the website owners as only they know why you have been blocked
As above: No-one in the community can tell you why you have been blocked and no-one in the community can unblock you, only the website owners can do that
You can try to look up (e.g. through Google) and see if you can find email addresses, social media links, or similar, and (attempt to) contact them through that.
Sometimes, a WHOIS lookup on the domain may give a link, where you can attempt to contact the domain registrant.
Even if you attempt to reach out via alternative channels, as mentioned above, you aren’t guaranteed that the website owner will take any action at all though. Any actions (or lack of same) will be at the sole discretion of the website owner.