I'd have felt an obligation to make the effort to help them, on account of how they paid me, and I'd ask them to clarify the problem. I'd use a tone that reassures them I'm taking them seriously, rather than one that gives them good reason to think I don't care about them.
Yes, their tone is rude, but it's not as if it's outright abusive. One can't be so thin-skinned as to take offence at punctuation. They also failed to provide any details about the problem, but that's what happens when you deal with customers rather than professional testers. The ability to file good bug-reports (or support requests) is a skill; you can't very well insist that all your customers must have it.
Yes, their tone is rude, but it's not as if it's outright abusive. One can't be so thin-skinned as to take offence at punctuation. They also failed to provide any details about the problem, but that's what happens when you deal with customers rather than professional testers. The ability to file good bug-reports (or support requests) is a skill; you can't very well insist that all your customers must have it.