Phone alarm not working.

Hiya, my phone alarm’s not working.

It doesn’t always not work so I can’t really test it or anything but here’s what I know:

• The alarm still comes up on my screen, it just doesn’t make any sound.
• The sound on my alarm isn’t set to “no sound”
• I don’t think it’s an issue with the hardware because I got a new phone yesterday and it’s doing the exact same thing (which really annoyed me)
• My ringer volume is very loud
• I don’t have or use any other alarm apps

I’ve missed quite a few important appointments & classes that I pay for so as you can guess it’s starting to really annoy me.

Thanks in advance for any help you can give.