If you are looking for advice... as a monarch myself, I can tell you, it does not matter who is in the wrong. It does matter who is in the power position. In the current circumstance, they are. So it is to your kingdom's benefit to swallow your pride and accept their CF especially if it is a simple CF and they aren't making any further demands. Cut your losses and focus on your current objective, your war. One thing kingdoms like these fail to realize is that the age is 10-15 weeks long, acting poorly this early can result in consequences later. You can choose to be those consequences, you simply need to bide your time. This is a strategy game first and foremost. Do not let your ego get in the way. Sometimes you have to retreat from a battle to win a war.