There is another function, sound_volume(index, value), which only affects one individual sound. You could try that, replacing index with whatever sound you are playing and value with global.volume. But also run the game in Windows and check if the global volume works. If not then these functions don't work in HTML5!
Nope nope and nope. None of that worked so I think I will just take a break and work on some other functions of the game and come back to this. Thanks for the help though too bad it didn't work.