Logging in

So my iPhone 7+ was stolen on the 21st and I put the lost mode on and now I have my new iPhone 7+ and backing it up to the old one and it keeps saying error when I try and log in, would that be because I put the other one on lost mode ? I backed the old one up around 7pm on the 20th and then the phone was taken on the 21st so now I’m wondering why it’s not letting me log in... what should I do ???