As you set forth the facts, under Rule 3070 the firm has to report the complaint and depending on the dollars involved, the settlement. http://rrbdlaw.com/RegulatoryLinks/uforms/30700401.htm
Your options are somewhat limited. You could seek to have the U5 material expunged, but that may be difficult if not impossible. You could seek to amend the U5 to include more accurate statements, if that is the case. You could sue the customer if you believe he defamed you or engaged in fraud (good luck, but it's still an option).
You should also review your U4 to ensure that you are now disclosing any "yes" answers that may arise from the U5 incident.