contest it, your allowed to park on double yellows whilst unloading (dependant on kerb markings) as long as they see you loading/unloading you entitled to 20 minutes. Also as said in a previous post information entered incorrectly usually goes in your favour as well. Lastly, if he didn't take a photo of the ticket on the vehicle and a photo of the restriction plate then they may well be stuck without proof (make sure you weren't caught on a camera )

HTH