I'm being billed for EC2 usage and I can't figure out why

The last two months I've gotten small, unexpected bills for EC2 usage. Both times it was for it was for SSD provisioned storage in the us-east-2 region. Both times I went and looked at the EC2 console for us-east-2 and didn't find anything -- no volumes, no instances, no nothing.

After the bill for September came in and I still didn't see anything, I went into the global view and clicked around and found two instances in Northern California that were stopped but not terminated. I've terminated those instances, and maybe that's what I was being billed for, but...well, I'm super confused?

First off the region is wrong if that's the case, and it caused me to get billed this month because I was looking in the wrong place. Second, I did in fact start some instances two months ago as part of an experiment I was running, but they were in Ohio, not No. Cal, and (I thought?) I terminated the instances when I was done. I obviously could be wrong about that too, but that's what I remember. Can someone at AWS help me? I'd like to stop racking up charges, obviously.