Stay strong! This is difficult for most people and that’s what they’re banking on. You are right to be angry and right in your request for a refund. You shouldn’t have to deal with their shoddy work and you already gave them more than enough of a chance.
I apologize if this gets rambly - When I was getting my accounting degree, we talked a lot about warranties because of liability/taxes/blah blah blah. The real take-home for me was that companies sell people extended warranties banking on them not being used. Companies literally try to view it as free money. THAT’S why they are so difficult to deal with when you have to cash in on that warranty. They don’t want to have to invest anything in their ‘free money’. The thing is, it’s NOT free money, it’s insurance you paid for when you got the computer to protect yourself from exactly this kind of bullshit.
I know it’s hard, but stay the course. Your feelings are valid and worthy. Get angry, be blunt. Don’t worry about remaining polite or likeable. Remember that they are essentially trying to cheat you out of the money you paid for a working product.
I believe in you!