How do i know you are not Phishing

I receive a call from someone claiming to be from Virgin asking me for my ID number and address and etc. <br> <br> I was not once told for the reason of the call and when asked I was told i must supply my details.<br> <br> I do understand you need to ensure you are speaking to the client but how do I know as the client that I am speaking to someone from VM and not some person trying to get my details.<br> <br> Work on another plan, im not just giving some random my details when they phone me. <br> <br> Teach your staff how to speak to people