Let them conduct their interview outside your premises, they need your permission to enter the house.Here we go. "Sir/Madam" and no name on the address means it just a generic spam letter.
I feel insulted that they think they can just set deadlines and ultimatums for me. Obviously I'm not going to actually speak to them.
Do not leave your door open so they can get a foot in.
However their next step maybe to get a court order for a warrant.