The agent that told you that it would not cancel within 24 hours was not providing information that is in line with CoC
The CoC prohibits making the hold in the 1st place - not that you could have held and called back in 6 hours , 12 hours etc
I wouldn't be assuming that the price would have been the same if you had waited until the evening
Your options are to either stay in premium economy or call when the account holder is available and pay the rate that is current then