Getting stiffed for providing professional services in good faith almost always ends with a feeling of regret including what you shoulda, woulda, coulda have done differently to have avoided the situation. Your question in particular asks what would be ethical ways to proceed. As an EA, you are subject to the Joint Board for the Enrollment of Actuaries and its Standards of performance of actuarial services which includes guidance on what is considered "records of the client". You also should be aware of the ethical standards of any professional organization to which you belong such as ASEA, SOA, ASPPA, AAA...
Generally, while there are differences between each organization's code of ethics, if you delivered work product prior to receiving payment for those services, you cannot withdraw or invalidate a client's reliance on that work product. Generally you do have a right, absent any formal contractual obligation, not to perform future services. You appear to have a direct relationship with the plan sponsors since you have filing authorizations and also because you personally sign the Schedule SB. If ultimately you decide not to perform future services for the client, you should notify them in time for them to find another actuary, but you may find in some of the applicable codes of ethics that you should not disclose the reason is the TPA did not pay your fees. If this is the case, consider offering to continue working directly with the client as a change in your business model.
Keep in mind that it is the TPA that is not paying for your services, but it is the plan sponsors who are using and relying on your services. The ways to proceed you listed have an element of vengeance or punishment which commonly is driven more by emotion, and it is the plan sponsors (not the TPA) who would suffer by attempts to remove the SB.
Temper the emotion, seek legal counsel about how to proceed about getting paid for services delivered, and get some guidance on the cost of exploring legal paths forward in terms your time and expense against the known cost of writing off uncollected fees.
Do take some time to implement, maintain and follow the terms service agreements and engagement letters with the TPAs and clients.