Let's take the customer's discount away!

I bought a Restonic King Size Tanzanite bed set on a discounted price on the Black Friday Sale in November 2022 and after only 14 months the mattress had a coil spring protruding from the side. Contacted Restonic, as the bed has a 2 year guarantee and 10 year warranty. They are happy to replace, but it has to be done through the store / store chain it was bought. As the product is defective, I have lost confidence in the specific product and would rather replace with a more superior product of the same brand and I am willing to pay the difference in current value between the two products. The problem: OK Furniture wants to write off my discount and let me pay in the full difference. Shouldn’t the difference be sorted out internally? The price I paid and the value of the item was for my benefit, wasn’t it? Now they want to take that away – or I must settle to replace the item with the same inferior quality product. And Restonic is still adamant that the store sort it out – but it is their product that is faulty. Beware if you ever consider buying Restonic or supporting the Shoprite group of companies.