Apple iPhone 12 Warranty Nightmare: Serviced Twice, More Issues, No Resolution!

I sent it to the service center twice, but they opened it up without Apple knowing and said I messed with it, so now my warranty is void. At first, they told me everything was cool with the device, but unfortunately, things just got worse. So, I sent the device again and they were like, "Yeah, the same issues are still there." Just so you know, I left my phone at the same service center both times. So, now I can't even use my device because they messed it up even more and haven't bothered to talk to me or fix it. It's on you Apple as your service center messed up my device and didn't fix it right. I intended to pay for a phone that actually works?