Not every daily reward will give an item. Sometimes it gives exp or mana or something of that sort. It's pretty easy to miss it if you were on one of those days.
If that's not the case and you're sure you didn't get anything, you can make a support ticket and get the reward. You will need proof that you claimed it and didn't get it. But since daily rewards are are small, I wouldn't bother if I was you.
I've never heard or seen someone miss out on a daily reward like this.