I was asked (some time back) for the "other part" of the V5C when registering a UK car here.
I explained that it consisted only of a set of tear-off slips, one of which was used for a change of ownership, in a similar way to the tear-off slip on the Carte Grise, and had no relevance to the car's registration.
I added that the other slips could be used for advising DVLA of the car being scrapped, exported, or sold to a dealer, and that I had discarded the rest of them after sending off the "export" slip, as they were of no further use to me.
That explanation was accepted, but that was by a person in our Prefecture.
If that is in fact the problem, I suggest you tell ANTS what the "other part" is, and also that if they do not understand you will approach SOLVIT to explain it to them.
On some great and glorious day the plain folks of the land will reach their heart's desire at last, and the White House will be adorned by a downright moron.
H. L. Mencken 1880 - 1956
Some may not like his views, but what a prediction!