Awful smell from underlay - what to do?!

Hi there, we recently had new laminate flooring installed in 3 bedrooms with an underlay provided by the fitter but as soon as the underlay came into the house it brought with it a terrible smell. The rooms are all finished and sealed now, skirtings back on, it has been a week and a half, I have hoovered the laminate multiple times and used zoflora to wash it but on checking left over underlay in our garage, it is definitely the culprit for this terrible smell. It smells like cat pee...
What can I do? The fitter said it could take a couple weeks to disperse. I've had all windows open wide 12 hours a day. I was worried it was formaldehyde "off-gassing" from the laminate but the spare laminate planks we have do not smell. They were the lowest VOC level laminate we could find (from Tapi) and it is the underlay that stinks. Please help!

was it sealed in plastic or just rolled up ??
my thoughts are "sweating " as its usually damp or moisture that magnifies the smell
avoid [do not use ]any sort off moisture to clean as that will need to evaporate iff trapped before the smell has any chance to disperse

What underlay is it ?

Maybe if was cat pee.