Money taken out of apple cash suddenly, without me spending it

I had $4.96 in my apple cash. I tried to spend $3, and my card got declined, so I tried again. Declined. I look down at my phone, and suddenly, I have $-19. I say "okay maybe it's a glitch," so I turn off my phone for a couple of minutes. I look back at my phone again, and now I have $-16. Does anybody know what's happening?