How do I fix this unknown charge?

I just looked at my bank statement and it says I have a charge of $8.11 from AMAZON PRIME AMZN.COM/BIL WA. I heard that it could be because of an Amazon prime subscription, but I haven’t been a member or ordered anything for two months now, the statement appeared a day ago most likely, since it wasn’t there on Friday or Saturday when I checked my statement. I know that I should call my bank and Amazon, but right now it is 1am, so I will call later in the morning, I just wanted to know if anyone can tell me if they had a problem like this before?