No Birthday?

My stepson J turned six about a week ago. My husband and I threw a big birthday party for him before he left for the summer to his mothers. We do this every year because he spends the summers with her so that means she has him for his birthday. Every year she promises him a big bash, presents, friends etc. She usually doesn't deliver but this year was different. This year she hyped up his birthday to him and then flat didn't give him one...That however was the only the first blow. She decides that he isn't available to talk to us on his birthday, then she calls a few days later and says if he comes home and complains he didn't get a birthday it was because everyone was busy. Those were her words! Too busy to throw her son a birthday!! When we asked why we couldn't talk to him she had the nerve to say she thought we did. I'm so glad we gave him a wonderful party, this to me just seems like the ultimate act of thoughtlessness and cruelty. Anyone else ever experience anything like this?