Call back to the toll free number and ask again.. that has always worked that I know of.. just call back and eventually, probably the next time they will let you pay to upgrade. Sometimes you get someone on those toll free numbers who is lazy.
cruiseplanner is a TA so keep that in mind. There are many great PVPs at Carnival too.
Id just call back asking to upgrade again.. ask for a supervisor. I always get what I want... sometimes on the weekend I have had to change cabins on a sunday, and had to call again... CALL BACK and talk to someone else.
If you are booked past guest rate you are not booked Early Saver rate. Rates cannot be combined, so its one or the other. Each is a specific rate with its own set of rules.