These days we certainly cannot depend on the EXP desk for knowledge that used to be a given in the past.

More than ever, know which flights you want and what the availability is before you call and do not hesitate to terminate politely and call back when you get the warning signs that you are dealing with someone who does not know their way around the system.

For the OP, yes, I would have expected you to be put on the flight with an open F seat in the circumstances you describe.