Setting up apple watch, asking for old Apple ID + server error

I've just bought a Series 9 apple watch (first time buying one so havent set one up before)

When I'm trying to connect it to my iphone it is trying to connect to an old apple ID. I havent used this ID in years and nothing apple based is connected to the email address.

I have access to the password and email its not a inactive account, i just dont tend to use it.

when trying to continue I am getting an error message saying it cannot connect to the server and there is no way for me to change it from that old ID on the set up page.

I have also logged into icloud on my laptop on the old ID and there are no connected devices.