How do I find out who are the registered agents of a LLC company in Florida?

I am trying to serve summons here and I did one, they stated they were not registered agents even though they have accepted numerous other service of summons and want to get the next one done correctly.

Is there a place where I can go look up who is doing this for this company so I can get going on it?

Welcome to AMHD; have you checked here? http://www.florida-registered-agents.com/

In general they are listed on the corporations filing with the state.

The Secretary of State Division of Corporations will have all the pertinent information you need to do a proper service. The registered agent's name and service address which the registered agent must be present during regular business hours Monday through Friday to accept service of process.