I went into my hero gallery to look at Genji's stuff but when I selected him my coins fell to 2800 from 3800. Does anyone know why this happened? I don't know if this helps but I play on Xbox One.
You must have accidentally purchased something without realizing it. If that's the case then there's nothing anyone here can do, but you should definitely contact their customer support.
This is a fairly common glitch in 2 ways.
If you commonly switch between devices a bit, or you have played on the PTR, when switching back to another device, you may lose coins or XP or other currencies. I don’t know why this happens. To be honest it is Blizzards fault.
This can happen if you have tonnes of coins and you have used about 1 thousand of it, the currencies can glitch out and you may end up paying less, or more than what you bought it for.
I know this answer is late, but I hope it helps.