C# how to make an API with a single entry point (service Class)

I have to make an API C# that permit VBA(Excel) to use internal ressources(like a DataBase). I have make a Class Services, that call methods in many others Class (book, music, etcc..). Ressource Classes have CRUD methods to use the internal ressources.

for Exemple i want the VBA devlopper to use API just by calling "My_API.Services.getBookNumber()" (for exemple).

All works properly, but when i try it in Excel, when i write "My_API." i could see all the methods directly without using my Service Class.

How may i resolve that ? i have plenty of Utility Class just for my API usage, and i don't want that the VBA dev use them ^^

ps : i use visual studio 2010 for customer's reason ...

Thanks for your help !