You should stop spraying until you have some sort of identification. How do know what kind of product to use?

You'll need to give us some more information about your Dwarf Burford Holly. How long has it been planted? What kind of drainage does the soil have? Have you had any significant changes to the environment that may affect the soil? Have you inspected the plant for scale insects or other pest problems. Are you losing leaves from all over the plant or just the new leaves?