There can be multiple reasons as of why, Some factors result in that case, Didn't clearly hear you or In the worst case didn't really bother, But they did know about your birthday didn't they?, But they were probably busy, But if it was directly said to them yet they didn't react, They can still be explanations as of why, But don't think about it badly alright?, This can lead to stress and depression, I've experienced this and it was not pleasant to having been misinterpreting what they answer and how they react, For example if I said, I have a crush and their reaction is not really interested, Then it may mean many things, An example of them being busy with something else, And will deal with that later, But the usual reaction is immediately excited isn't, So it's just a analysis of your situation, Maybe have a talk with your parents