So I've tried to update the device, or - to be more specific - downgrade it from android 6 to 5 with an official firmware to do so. When I started, phone was at 100% battery, but the process bar got stucked for about 30 minutes at about 20%. I decided to turn the device off, in hope to just reset it, but it didn't turn on again.
when I hold the power button, i do feel the 2 vibrations, like I normally would when starting the phone. the screen stays black and nothing happens.
I tried to hold vol down and power, as well as vol up and power, but neither worked. How can I restore the phone? I don't mind loosing data - I've backed up everything yesterday.