So, some updates:
The level 2 complaint was sent in as advised and an auto reponse was received on 9th April (aiming to priovide response in ten days etc)
then another email from DVLA arrived on 2nd May - attached below (mentioning complexity of the case, requirign more time etc)

then today, this, in the post.


This one is a little threatening, the money is going up and debt collectors are involved.
Naturally getting slightly worried etc, which is, i'm sure the intent.
Any help, clearly, very much appreciated at this point.
Thank you all