Typically, Only KYC is the only way to recover an account that lost 2FA since a hacker can get all those supporting details by compromising someone device.

But I think a sign message on the receiving address for the withdrawal can be a substantial document to claim ownership to your account.

However, Freebitco.in support ticket is very slow to respond. Your best chance to wait CSFB account to become active again here and handle your case.