This supplier really is an unethical company, aren't they? I mean, when you approach a retailer for a quote for a product you do not expect that retailer to be got at by a manufacturer, to ignore your specific request and give you a quote for a different product. For two retailers to do the same sounds very dodgy indeed, as it sounds close to being a cartel (which is illegal).
Edited to add:
Under sufferance, and not because I agree one bit with it, I've edited the above to high light the intention and added the text below for the avoidance of doubt:
The observation I was making here, and which has attracted criticism much later in this thread, was that a builders merchant had been approached to quote for a specific product, with specific performance parameters relating to thermal resistance, acoustic insulation properties and decrement delay time. Instead of offering to supply a product, or an alternative that met all the same performance requirements, it offered an alternative that fell well short of meeting the acoustic and decrement delay requirements. I consider that to be unethical behaviour by any company, whatever they are selling. For two different suppliers to do the same thing seems to me to raise suspicions as to who they are really serving, their customers or their suppliers.