I have that MiA1 since 1 year. Often when I call these times, it's impossible to hang on. I have a black screen and no possibility to act, to do something. Even the buttons don't work. I have to wait that the other one stops the call, and it's a big problem, when on the other side I leave a message, I can't stop the call at all.
Last time I had to push on the side button 10 seconds long to enter fastboot mode. Pushing butons don't work, even stop or back buttons, nor volume buttons.
Did you ever have that problem? Did you find a solution?