@t0mb0 I have similar and went for a £5 black plate that bolts on to rear behind towball which I spied when I was in the towbar place. Guessed it would provide some protection to bumper as caravan has habit of moving forward when unhooking.
Unless you are on a slope and haven't put the caravan brake on properly, that's user error. Reversing the caravan compresses the Alko hitch, so when you unhook, the hitch will creep back out and crash into the rear bumper. Next time you reverse park, go back 6" further than you need, then pull forwards a touch to pull the hitch back out.