Oracle - of all businesses - got this right. I know, I'm in shock too.

In Oracle Cloud Infrastructure, after your credit is exhausted, you have to explicitly opt in to billing or else they stop all paid services for you.

Moreover, you can choose to keep billing disabled and use their free services without fear of unknown costs.

AWS have just decided to run with a policy of offering refunds when people make mistakes. Unfortunately, some people are ignorant of this, or too timid to ask for their money back.