by double socket do you mean like this
if so have you tried using the test socket (black arrow) with a filter and see if that works if not then problem outside your home
as long as nothing at test socket then should not be charged for engineer visit
@Paulr7894 I'm sorry to see you're broadband is broken. If the helpdesks have identified your fault needs a visit no further diagnostic checks are done until the engineer arrives as the helpdesk have likely established that it can't be sorted remotely.
Unfortunately all you can do now is wait until the engineer visit for further progress to be made and I am sorry for any inconvenience caused in the meantime. Post back to let us know how the visit goes.