I cannot sing out of an old iphone X

I want to erase the content from an iphone X i use to have and I cannot. I removed it from my I cloud account and asked to erase it from there but when it did not happen.

When I want to erase it I get the following message: Verification failed. The operation couldn't be completed.[AK Authentification Error error - 7005].

If I want to sign out from the apple id i get the following message: There was an error connecting to the Apple ID server.

I just want to make sure all the data related to me from this phone get's erased. How can I do it?

Thanks