take your new TV with you to your daughter and compare the image quality and the settings there. If it keeps being poor, you've got a good reason to complain.
I've been a fan of LG for many years. I prefer it above brands beginning with Sam and Son.
My daughter purchased an LG 4K TV last year and for the £400 price point the picture is amazing. The upscaling is really near 4K. You can see the real difference. Based on this we choose to buy an LG 4K TV at around the same price point. It's not exactly the same model but I think it's the next model up as it has a couple more hdmi port's.
The picture quality is noticeably poorer than my daughter's model. We both use the same Freesat PVR boxes. I know this as I bought them and she took hers with her to her new house.
We we're over at hers last night and watched House of Cards on Netflix in 4K. Fantastic picture quality, bright, clear and sharp.
I came home and viewed it on our 4K TV and it's noticeably dull as though just standard HD not UHD.
Some might say it's your broadband but I don't think so as we're on 150mbs.
Do I go back to John Lewis and complain?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic