I tried to contact the freebitco.in staff and they sent me a link that takes me to this page, how do I change my freebitco.in email here?
You can't change your email address here.
They have probably asked you to sign a message from your bitcoin address to prove your ownership of the account. This topic is only a guide on how to sign a message.
The first requirement for signing a message from a bitcoin address is that you must have full control over that. This means that the address has to belong to a non-custodial wallet.
If an address belongs to an exchange or any custodial service, there is no way to sign a message from that.
Do you have control over one of the addresses you deposited from? Where did you deposit from?
Or do you have control over the address you set at your profile? Where does that address come from?