Penalty charge for a motoring offence (stopping in a box junction)

I'm not angry just confused why they didn't volunteer the information, I'll give them another call later and perhaps I'll get through to some who can help a bit more.

Hi, I received a Marston enforcement notice for a previous tenant (moved out 8 months ago). I called them up (I have dealt with other bailiffs regarding this tenant) and explained that he moved out 8 months. they wanted proof that he had moved, ok so what do you need - they couldn't (wouldn't?) answer the question and kept saying I needed to prove it. How do you prove a negative? they said they will send enforcement officers. Do I really have to go through all this or is there a way to call them off? The other problem is that I work away a lot and they could potential gain access without my knowledge eventually.