Frustrating I know. The banks have this down to fine art - they call and expect me to give them some identity check info so that I can prove who I am before they can continue the conversation. Before complying, I request some ID check from them, so that
they can prove who they are and are not scammers trying to get my details. Deadly embrace

They generally have no way to prove who they are - but more importantly have no concept of any requirement to so do!
Perhaps this is an important area that PlusNet need to address.
Maurice