I have never in 9 years working with AWS - four at product companies as the architect, 3.5 at AWS itself working in the Professional Services department and the last two working at 3rd party companies - ever heard or read about anyone either on a personal project or a large organization not be able to get a refund or in the case of a large org, sometimes a credit from AWS when they made a mistake that was costly to them.

I haven’t even seen reports on subreddits

AWS and all of the other cloud providers gives millions in credits each year for migrations and professional services for both their inside professional services department and third party vendors. The reputational risk for them to go after some poor student isn’t worth it to them. The same is true for Azure and GCP.

Have you read one even anecdotal case where AWS didn’t immediately give a refund to a student who made a mistake just by them asking?