The next time, if so desired you may let them know that you charge $______ per minute/hour/incident for your time and ask if they wish to proceed. Have a NOTICE prepared ahead of time to hand to them that indicates; All Rights Reserved, No Consent to being detained, fee schedule and any other lawful demands. Carry a receipt book and write up a bill on the spot. If they laugh or don't accept it, mail it to them as one would be mailing a follow up NOTICE anyway stating that they have a a certain number of days to pay or the amount increases. Sound familiar? Equality under the law is paramount. Mail may be sent to them at their office. Amounts up to $7500 may be pursued in small claims court (Neither party may not be represented by an attorney), higher amounts in State or Federal court. Since they are acting in their official capacity they can also be billed through their Risk Management department through which they are bonded. If enough claims are made one loses their bond and can no longer be employed with that agency and most likely ever again in a position requiring bonding.
There is a process in which one may make a claim against another and secure a judgment without an attorney.