I cannot get into my iCloud account

I'm trying to get into my iCloud account on my new Macbook. However, when I try, it asks me to verify with a code it can send to either my other Macbook (which no longer works) or to a phone number which I no longer have. I would create a new account, but whatever new id I type, it just says "You cannot create a new account with an existing id", and tells me to log into my old account, which I can't do.