Esteem Auto Sales (Ernest & Verne Mey) have no integrity

I viewed a car at Esteem Auto Sales that I liked in January 18. The car looked really nice and I was interested in it, but I noticed that the car (Honda CRV) was missing the standard Cargo cover that these cars usually come with. I pointed this out to the salesman (Verne Mey), who assured me and my father (also present) that if I purchased the car he would be able to source a cargo cover to make the car complete. I told Verne Mey that I was interested in purchasing the vehicle, but that I wanted a better price (as you do), Once we had come to an agreement on the price I stated the price INCLUDES the cargo cover. He agreed. I went home that night and thought about the car, and decided I wanted it. I wrote an email to offer to purchase. The very first line of the first email is "Hi Verne Ok, I’m going to go for this deal for R***k, but I want the rear boot cover." (This is copy pasted straight from the email.) I go on to mention in that same email, that I would like to pay right away and take delivery of the car the next day, with exception of the boot cover which may understandably take a few days. Verne and Esteem Auto Sales agreed to this deal replying to the email with "Perfect pop over Asap with your Id and proof of address for the licence and reg, Will try sort cover Asap."

I paid the full price and took delivery of the car in January, it is now July and Verne and Esteem Auto Sales ***ner: Ernest) refuse to find or purchase a cargo cover for the car as they agreed to in the offer to purchase and verbally. They are claiming that they never agreed to getting the cargo cover for the car, but that they would only look to see if they could get the cargo cover from the previous owner. I have tried multiple time to get them to stick to there agreement, but they refuse.