Hello!
This website, much like the old official version, does not hold an option to remove an account from the user's side (as any videogame with database connections doesn't, e.g. Genshin Impact, Wuthering Waves, Fall Guys, Fortnite...). The website, to host the highscores, the Winx Adventure game and have all this customization with the Web Avatar has a lot of custom scripts attached to an account that makes termination very hard on our side, as we're forced to go throughout multiple columns in the server just to delete your data and pray we don't accidentally mess with someone else's, hence why we usually accept terminations only if the registration was a mistake, as stated in the welcome email (if a person didn't even touch the account, deleting it is very easy)
That said, if you can provide an answer as to why and you really want to, I will delete it.
I just read your email and you said you want all your data deleted completely with no trace, but at the end of the day, the only data that truly gets stored and you can be concerned about is email, username and password, everything else is just "visual pollution". The server is extremely well protected also and has been around since 2012 in different platforms and no hacking issues ever happened, if that's what you're concerned about.