Yes, I submitted my amended defence last night, filed with the court and served on DCB. Then this morning the N279 landed from them.
Massive thanks to you all.
To me it looks less like something they only spotted late and more like a claim they were always prepared to drop the moment I actually stood up to it. They've known about the orphaned payment from the very beginning, so seeing my amended defence was likely the point they decided it wasn't worth the risk. The timing is telling too - discontinuing right on the deadline, the morning after I filed, rather than at any of the earlier stages where they had the same evidence in front of them.
I didn't find a "pay the fee or you'll be liable for costs" line from them. But I did flag CPR 27.14(2)(g) to them twice in writing, once in my pre-action reply and again in my CPR 31.14 request - warning that if they proceeded unreasonably in light of the evidence I'd ask the court for costs. I also enclosed my bank statement, their own VRM entry log, and the gov.uk proof that incorrect VRM isn't a real vehicle, all pre-action. Their replies brushed it off ("absence of evidence" and they proceeded anyway, then discontinued on the morning my amended defence was due.