I Regret Buying a Samsung 18000 BTU Air Conditioner That Does Not Cool

I bought a Samsung 18000 BTU air conditioner less than a week ago, and it's already having trouble chilling. To make things clear, when I use the remote to reduce the temperature to 20°C, the unit first indicates 20°C, but then it goes back up to 25°C on its own after 5 seconds. This means that I can't obtain the cooling I expect from a brand-new item. As soon as I saw the problem, I called Samsung support, but I haven't gotten any useful aid or a remedy in the last week. I choose Samsung because I thought it would work well and have good customer support, but so far, that hasn't been the case. I hope my issue will lead to a quick solution.