Apparently recycled polyurethane foam is the standard underlay for carpets; it supposedly has some benefits but sound insulation of any consequence doesn’t seem to be one of them. It seems that when dealing with the sort of people who demonstrate disregard of laws and decency it’s an error to declare the end of major combat too early; better to presume that they haven’t even bothered to read the detail of any finding against them (or even that they can read). It’s easy to imagine them thinking and gloating that putting in the cheapest, thinnest carpet gives them the final victory. If you can persevere and get another of the cheapest carpet on top of the smooth one currently laid it may be a suitably just outcome.
The pleasant and polite couple in the unit above mine seem to have a hobby of lifting up their stove to ceiling height and dropping it; more likely I’m guessing it is heavy duty exercise equipment, perhaps including dropping 50kg bar bells onto a rubber mat.