I’ve Been Ignored by the Service and I Need a Replacement or Refund Urgently

I bought an iPhone 15 Pro from Media Markt in December, and I've had issues with it since day one. It’s been sent for service four times, and I’ve barely been able to use the phone. The fast charging doesn’t work properly, even when the phone is turned off, and it overheats frequently. I’ve been trying to reach the authorized service and Apple support for days, but Basari service never answers calls, and the direct line is always busy. Media Markt doesn’t stand behind the product it sells, and the Apple staff have been unhelpful, with no one taking responsibility for my case. They fail to call during or after the scheduled appointment times, and there’s been no response or attention whatsoever. I never imagined I’d spend so much money and be treated so poorly. I urgently need a new device and request a replacement or refund as soon as possible. Additionally, the billing date and the start-of-use date shown in the device’s settings don’t match. If necessary, I will file a formal complaint.