Is that a letter through the post?
Yes, and they rely on the name and address on the V5 Registration Certificate for the vehicle to send it out.
So are you the owner, and is the address on the V5 up-to-date in all respects ?
The point here is that under the legislation, the owner of the vehicle has responsibility for paying or appealing all PCNs against the vehicle, and may not have been the driver at the time. So whilst they may have sent you a letter of rejection, they still have to send the Notice to Owner to the registered owner of the vehicle.