Can anyone help me? My i cloud account is inaccessible. Changed password. System updated. No joy.

My mac.com account that I've had for nearly 20 years has, for the first tim ever, started to have log in issues.

I have done the latest system update.

I have changed the password.

I still can not log in to my account.

I have reported it to Apple a few times, but have had no response.

Is there a UK based telephone customer care service for Mac?