There's a law for that. If Coinbase did not require an external bank account to create the coinbase account, by law, they cannot require one to close the account. At least, that is what I have been led to believe. You could sue.
You’re giving legal advice based upon something you were lead to believe. That’s the first problem. The second problem is that proving damages would be difficult. The third is that you’re operating in a pay to play justice system.
Maybe you don’t have to make comments like this?
I have to admit I'm always baffled by these "you could sue over this trivial matter" replies. Do you think lawsuits cost no time or money? Obviously I'm not going to do that.