Make a phone call at this point. You say you don't want to be unprofessional, but the agent seems to be operating under no such scruples.
Calling is professional, and as a client, you are allowed to make the call. "Hi, Eowyn, it's me, jackbenny! Just wanted to touch base since we haven't been having a lot of luck talking via email."
If that doesn't help, then I don't know what to tell you. Look at your contract and see what your options are for cutting the agent loose. If there's a clause saying you have to give the agent a letter outlining your grievances and giving her thirty days to get her act together, it might be time to send that letter.