Xiaomi Made My 15 Ultra Unusable With Muffled Call Audio

Xiaomi 15 Ultra mobile phone sounds muffled after the first 3 minutes of talking, as if my voice was pressed on the pillow. I used Xiaomi 10 t Pro, which I spoke fondly for 4 years. I wanted to switch to Xiaomi 15 Ultra phone because I was satisfied. I also bought smartwatches and kits while doing this. But whatever systemic error the phone was produced with, it disgusted me from this brand. The main purpose of the phone is to communicate, but on this phone, people are constantly muffled. It cannot be spoken, your voice is coming from behind. The strange thing is that I sent it to the authorised service called Mieko on 11.07.2025. They reported that the product was maintained and passed all tests successfully. The product has not even been used for 2 months yet. Please either change my phone or refund my fee. I want to maintain my belief that a well-represented brand like you in the Turkish market will not victimise the customer.