I have done some digging about. Assuming what I have found is correct, up-to-date and relevant, here goes:
AA Insurance branded policies are administered and sold by Europa Group.
The reference to 4D is (as Wessie says) probably only relevant to claims. You are not making a claim, so they can probably be ignored.
Somewhere in the blurb you received with your policy, there will be a sheet of paper which maybe looks a bit like this:
It might not be exactly the same but it’ll tell you how to make a complaint. The relevant section may well look something like this, taken from the document linked to above:
As you can see, all roads lead to Europa Group. The complaints telephone / contact details are given in the screenshot.
But, you are not yet at the formal complaints time. All you need is the number plate change corrected.
What to do:
1. Call or contact the people you made contact with to request the change in the number plate. It seems from post #5 that you told someone about the change, but they simply forgot to register it. Or maybe they did and you are perhaps muddling up some papers.
2. Anyway, it doesn’t matter. Go back to the people you started with. Will they be open 24 hours a day? Probably not. Call them in office hours.
3. If for whatever reason course of action 2 fails. Try calling the number in the screenshot above.
4. Whoever you speak to, always have to hand:
A. Your full name, address and post code.
B. Your policy number and any reference numbers contained in the blurb you received.
C. The policy inception date ie. The date from when it started.
D. Your own contact details ie. phone and / or email address.
Having A to D ready will save you scrabbling about looking for them during any calls you make.
Let us know how you get on, please.