I Sent My Xiaomi Phone for Warranty Repair, and They Blame Me

I took my Xiaomi phone to an authorized service center under warranty, only to discover that I was the culprit! I'm just an office worker, and I noticed that my phone had a curved back despite the fact that it was sitting on my desk. I sent it in for repairs, and they refused, claiming it would cost me a whopping 1,680 tl to fix. Then they ask if I want to take advantage of a promotional offer. When I say yes, the price drops to 1350 tl. Now all I want is my phone back, but it's been two days and no one has called or provided any information. I make an attempt to approach them, but it is impossible. I simply want some answers. This entire situation is vexing, and I hope it is resolved soon.