Button calibration failure on HTC One M9?

[AC Question]

Hello there! I've had an HTC One M9 for about a year and a half now. Yesterday I realized the power button had stopped working properly - I couldn't lock the phone or turn off the screen. The volume buttons still worked correctly, lowering and raising the volume as they should.

To try and rectify this, I thought I would reset the phone to factory settings, so I entered HTC Download Mode (the one with the black background) by holding the power button and 'up' volume button. This worked fine. Once in download mode however, I was unable to navigate the menu with the 'up' and 'down' volume buttons (i.e. they are not working). The power button worked fine but I could not select any options as I can not navigate to them.

In another attempt to fix whatever has gone wrong, I rebooted the phone to the download mode with the white background by holding down the 'up' volume button and power button again. This time when I got to the menu, weirdly enough, the buttons were switched around! My power button allows me to navigate down, my 'up' volume button allows me to navigate up, and my 'down' volume button does nothing.

Is there any way to fix this or is my phone a lost cause?