Bluetooth issue on iPhone 12 mini

I have an iPhone 12 mini since May 2021 and having trouble staying connected to any bluetooth headset when on calls - normal or over the internet (like WhatsApp or Teams).

When I am listening to music there is no issue at all, but whenever I am on calls bluetooth keeps disconnecting and connecting every second which doesn't allow me to even hear the other person.

I have been talking to the apple support, they did all the troubleshooting, they have installed a profile on my phone and asked me note down timestamps whenever I faced the issue, which I have done.

Apple support experience is the worst. They try to call you just once, if it doesn't connect, then they do not even try to call you again. This is my worst iPhone and the experience with the support for such an expensive phone has been the worst. No-one has been able to help me and resolve the issue. I dont know if they even intent to, but I am looking for a solution from this vast community, so kindly help.