To directly answer your question, yes you are still billed for the Hobby plan even if you have nothing deployed, since it is a subscription model, same way you'd still be billed for a month of netflix even if you didn't watch anything that month.

You should be able to go into your billing page and click the refund button directly on the invoice in question, if you don't see a refund button then I'll private this thread!

https://railway.app/account/billing

It's confusing to combine a usage-based pricing model with a flat subscription fee–the way it's currently presented it seems as though the flat fee of $5 covers usage up to $5–and any usage above that incurs an extra charge. Given this, my expectation was that 0 usage would result in $0 charged.