Most schools block certain games, Especially social game where you can talk to other people without a filter. This is for the child's protection, If the administrator/Tech people has blocked it they have done it because they were told to by their boss and sadly can't do anything about it for its their job to keep the children safe and off of websites where they could be corrupted. Mainly they do mass blocks on anything that happens to come under 'games', sadly the login must have fallen under this.
I understand this is frustrating but its their job to do this. You can login on a mobile device however, Possibly borrow your parents phone to do the login or use your own. Other then that there is nothing else I can think of to help.