Hillary's Blinds

When was the contract signed. There is usually a 'cooling off period' during which it may be cancelled without penalty.
Sponsored Links
I will keep social media on the back burner for now
Exactly the opposite I would do.

And try watchdog on tv. The more people who go public about sharks like these the better. Sorry for your parents, makes me hopping when hear about stories like these.
Can you get a price for a similar blind from someone else? Price to include fitting.
They don't have to do a site visit if you find a similar/same type of blind and give them the sizes of your grand parents blind.
If the quality and price are similar then there's probably not much you can do. However, if the quality is the same but the price is much cheaper you may be able to alert Trading standards or some similar organisation.
Sponsored Links
You could handle the complaint via Resolver https://www.resolver.co.uk/ that way it's all tracked and done via email. Looking at the workflow for Hilarys, I'd say there's been a lot of complaints already. In particular you can select Price > Sales Rep Misled or Price > Rogue Trader.