This post has made me feel really poop. It is my exh turn to host Xmas this year. I have spoken with the children via txt today. They were happy, I was happy, but now apparently I'm a terrible parent :(
Clearly you're unhappy with your ex and therefore everything he does will annoy you.
But I'm a great parent, I love my kids above all else in the world, and txt is a perfect, non intrusive method of communication with children on this busy and emotional day. I don't want to spoil their day by getting sad, but I do want them to know I am thinking about them. Maybe your ex thought like that too.
My kids love cash and vouchers above all else, as it allows them to make choices. Most kids love choosing, just show them a catalogue or web page and watch them glow :). Maybe your ex gets that too.
Sorry he hurt you by leaving, but if he wants to be part of his children's lives you need to encourage and enable this, even if it's hard.
Judge me all you want, but in this particular circumstance I think you are wrong to take umbridge.