How to investigate/report mobile phone call bug

[StephenG1CMZ]

It has been suggested elsewhere that a press on the mic key is designed to play music or trigger Google Assistant, something I was unaware of.
So the fact that the Huawei seemed like it was prioritising music playback over making calls and playing music unexpectedly is no longer mysterious.
It can all be explained by a dodgy mic lead - which I would have considered had it just been hanging up.

Who would have guessed that pressing the mic key would play music rather than record sound?