AWS send me an invoice

Hy!
I use aws since 2016.04. with 1 instance (free win2012)
Until last week i doesn't get any invoice, but this day i got an incvoice with a few $.
Not too much the price, but i don't get it why send me this the amazon.

One thing changed two weeks ago, I setup another free win2012 instance.

Maybe this new instance made the "problem"?

Have you tried to contact their billing support?
You might have gone over the free allowance.
Nobody here knows why you were charged, you need to speak to them.

This happened to me once. I contacted then and asked. They told me why and got rid of the charge too

thank you, i will try it!