"When I asked Ms Li for help in finding my size, she told me that she was busy and that I needed to look somewhere else." ** there's no word called "servicer". A person who provides a service is called "service provider". In this context, you can either omit it (like I did above) or refer to that lady as "service-lady/woman".... however, it doesn't sound good in English. Not sure what Ms Li's designation should be....you didn't mention whether it's your shoe's size or size of your dress etc. Anyway, you can also call her an "assistant" or "shop assistant". ** usually, if the person is just giving you a reply, and he/she is talking straight to you face to face, just use the word "told"..... not "informed". In this context, Ms Li just gives you an answer.... she doesn't provide any "information".