You don’t get to post on a public board and then complain when you don’t like what you read. You’ve posted nothing factual which suggests a scam. So I’m going to assume that your kid is behaving honorably in the absence of evidence to the contrary.
Post a fact that is evidence that your kid is trying to scam you- and you’ll get plenty of suggestions on how to handle that. But right now all you have is suspicions about your ex (which I’m sure are totally fact based) and some allegations about your kid (with no evidence). Your kid doesn’t completely understand how financial aid works with divorced parents? Join the club. Millions of folks in America who don’t understand it either.
Have a nice day.