Substitution goods and refusing a refund

I spent £750 in Basingstoke Ernest Jones shop buying a pearl necklace and earrings. The earrings my wife viewed were not the ones we left the shop with. The earrings we looked at were substituted for a non-matching pair; one is longer than the other and they are different colours. Two weeks later, the store manager declined a refund on the basis of the earring having been removed from their plastic bag, which apparently invalidates the refund. This was not explained at the time of purchase.
Substituting duff jewellery having viewed the best items is probably illegal. Then refusing a refund is rogue practice. Shoppers need to be warned of Ernest Jones disreputable conduct and policy.
Ernest Jones business of showing nice jewellery and then substituting poor supposed equivalents is a rip off. They then refuse a refund on the basis of the goods being removed from a plastic bag thereby selling low quality jewellery and premium prices. Watch out!