I've had both of these calls Kiplet. The call regarding my National Insurance Number was only yesterday morning and I hung up on that one.
A couple of years ago I recieved one regarding a washing machine service agreement. I asked for them to quote the address for the agreement and they quoted my previous address! I had never had a service agreement on that washing machine either and left it there when I vacated the rental property. The name of the company was very very similar to Domestic & General, so I emailed them to alert them of the scam; I do have a service agreement on an appliance with D & G and I was concerned that there had been a breach in their security.
I haven't heard from the scam company since though.