You should request a full and unconditional release from the listing agreement.
If they do not approve, call you state's real estate licensing board and lodge a complaint.
If this answer was helpful, please mark it as helpful or as a best answer. This answer is for general education purposes only. It neither creates an attorney-client relationship nor provides legal guidance or advice. The answer is based on the limited information provided and the answer might be different had additional information been provided. You should consult an attorney.
Look at your listing contract to better understand your rights. Demand a full release from any obligations you have under the listing contract. List with another agent. If you are still unsure how to proceed, retain a lawyer in your area to assist. Good luck.
Your agent should have entered into a signed listing contract with you; that's required by Wis. Admin. Code s. REEB 24.08. He or she may have also violated s. REEB 24.09 by misleading you and s. REEB 24.17(1) by stealing your documents. You should consider filing a complaint with the Department of Safety & Professional Services: http://dsps.wi.gov/Complaints-and-Inspections/Complaints
The complaint to the regulatory board is appropriate, but if you are sure you have no listing contract or obligation to that broker, seek to list with another broker. Hopefully the new broker will meet your needs.
Contractually the prior would be liable to you for "damages" but the burden of proof would be on you. Likely difficult, if not impossible.
Lucky for you there are no papers signed with the prior, as if papers signed you might have not been satisfied with this broker's efforts (and stuck between a rock and a hard place); perhaps this broker just discovered he had done so much wrong according to rules that regulate this broker? In any event you are now free to go elsewhere and obtain the best you can find.
Note: no professional has any obligation to list your property or work with you; it is up to the two of you to agree.
Hope this reply has been helpful.