Xiaomi 15 Ultra Faulty Microphone

I am using a Xiaomi 15 Ultra Global version purchased from Best Mobile Phones in Melbourne, Australia, and for at least the last six months I have been experiencing an intermittent but persistent call audio problem. During calls, other people frequently report that my voice is very muffled or that they cannot hear me at all, which makes normal phone calls unreliable and often impossible. I contacted Xiaomi customer service and followed all the software and hardware checks and suggestions they provided. I have tried many different remedies and troubleshooting steps, but none of them solved the issue. In the end, I was told that it must be a hardware problem. The difficulty is that I now live in another state in Australia, and if I send the phone away for inspection or repair, I will be left without any phone during that time, which is not a viable option for me. Given that the problem has been ongoing for months despite all suggested solutions, and that it appears to be a hardware fault, I request that a replacement Xiaomi 15 Ultra Global version be provided to me. I am asking for a practical solution that does not leave me without a phone, and I would like Xiaomi to offer a replacement device so that this ongoing call quality issue can be resolved permanently.