Is there a fine for failure to update details from the dvla do you know?

Hi Guys I am new so forgive me if this is a simple question:- I have recieved a parking ticket / mickey mouse invoice from G24 a couple of weeks ago. I literally have a day or so to decide if i want to pay the 75 or fight it! I have read up on G24 and so i know that its unenforceable etc, and that they would have to take me to court but more than likely wont! I was the driver, and i was there double the allowed time, but either way its a new system to charge the parking in the car park this happened and i certainly didnt see the signes or i wouldn't have parked there! The twist in my situation is that they sent the letter to my old address, which means that somehow when i moved (nearly a year ago) i obviously didnt change my details! I remember trying to sort it all and my drivers license is correct so undure what happened there. So firstly, i dont want to start causing problems if in fact i have broken the law by not checking that the dvla had my car registered in the right place. And secondly, i would worry that G24 might send debt collectors to my mum and dads house, where i lived previously, as i'd worry that they would be able to talk their way around my mum and potentially get some money out of her should they pay a home visit. Any advice here would be great - ie whats the fine for not informing dvla of a change of address? Thanks Simon