Do I have a right to be annoyed?!

Me and my children's dad split 3 years ago and we have shared custody. Normally when it's one of our children's birthdays we both see them regardless of who they are supposed to be with that day. This year their dad has decided he won't be there for his daughters birthday because he's "too busy" he's also tried to make out to my daughter that me and my new partner won't let him see her, this has never been the case to the point that over the last few weeks I've constantly tried to arrange thugs with him. This morning I tried ringing him several times just so he can at least say happy birthday to her yet he didn't speak to her until almost this evening. He doesn't work, he spends his time doing what he likes yet he's too busy to ring his daughter?!

On top of this my sister couldn't even ring/text to say happy birthday either, we're not particularly close but I've always made sure that when it's my niece and nephews birthday I go see them. I even received a text message off her ex husband as he stills thinks of my children as his niece and nephews. This evening I received a phone call from my mum telling me that my sister had dropped off a present whilst we were out which I'm grateful for but why couldn't she ring or text herself?

Am I just being over sensitive or do I have a right to be annoyed?