I'm confused. Moving the joystick up and down and pressing fire to select the answer when they appear is how it should work. Also it is the letters next to the answer which you use on the keyboard to choose the correct answer. 'T' for top, 'M' for middle and 'B' for bottom. It's from a famous gameshow in the UK called Strike It Lucky. The only in game key is the 'M'. Left and Right in-game is 'Q' and 'W', these cannot work to select answers as I've assigned the other keys. I know for sure it works fine on keyboard as I tested it out today and it works as it always has. So I'm not sure what's happening with your version. How are you playing it? Emulation or real hardware, and if real hardware which mode of the Spectrum?
I think it has issues with +2. I remember someone mentioning another older game was not working correctly with their +2. Maybe try emulation and see if that works better as you can select the model. I think it's fine with a basic 128k machine. Not sure about +3. Unfortunately I believe it's an AGD problem so not much I can do to fix it.