For billing questions you need to contact Support. This is sensitive information and they’ll check it for you.

You can go to Billing settings (or manually by logging into Control Panel, click on your profile image in top right corner, then Settings and on left select Billing)

Scroll to the end of page and you should see list of invoices and payments. Open invoice for October and you’ll se your usage.

Make sure you destroyed Droplet. Power off is not enough, you’ll be still charged when it’s powered off. That’s because resources are still reserved for your Droplet.

Also make sure you deleted all Snapshots because as of October 1st they’re being charged $0.05/GB/mo.