Thank you for your patience.
-You are only required to remain at the scene of the accident and to provide your name and address. if the accident has caused any damage or personal injury.
-The prosecution must prove, beyond reasonable doubt, that injury or damage was caused.
-If there was no damage or injury, no duty arises upon the driver to stop and/or report so you can't be found guilty of failing to do so.
-If damage is shown, the burden passes to you to show, on the balance of probabilities, that you did not know that there was damage.
-You will need to argue that it was a very low-speed impact at a carpark. (In legal terms, it is called low-velocity impact or LVI). You will need to say that you inspected both vehicles, and there was no visible damage
I suggest you reply to their letter to explain all the above.