No accountability, stay away

If I could, I’d give them a zero. I booked them for a diagnostic on my car which was making a whistling noise. They sent their machanic who diagnosed my car incorrectly. He said the issue was the turbo. He was not convincing at all, so I sent my car to Hyundai. They picked up that the exhaust manifold was missing some nuts and just supp**** the nuts and secured the exhaust to fix the problem. Imagine if I had taken their diagnostic and replaced a rather expensive turbo unnecessarily. Anyway, went back to them to demand a refund but they have refused, insisting they have diagnosed correctly.Even after sharing the diagnosis from Hyundai. I’m disgusted to say the least, no accountability, just incompetence.