Their emails are confusing, but they came after the alleged violation in private communication, not what you were going from at the time of the alleged violation. If you ignore them momentarily (surely you understand they probably aren't as well-scrutinized by lawyers, which would explain why they appear to mistakenly refer to the tax status of the recipient rather than that of the donation), is anything else actually confusing or inconsistent? Their policies, the relevant laws, and what common sense would have you expect - they seem pretty cut and dried. Are they inconsistent with anything other than their emails, which came after the fact?

From another angle: why/how do you feel the tax-exempt-mess of the recipient itself could sensibly be the determining factor here, rather than the taxability of the transaction itself? Is there any law or precedent or anything outside their emails that would suggests a payment processor should look at the tax status of the recipient rather than that of a transaction?