What is difference among a Call Center Agent, A Contact Center Agent and a Customer Service Agent?

Call center agents make call to customers while in contact center customers call for complaints, inquiries etc and a customer services agents mostly directly deals with customers in physical.

Customer Service is broader field than Call center.... Call Center Agent deals with the customers over the phone (inbound calls or outbound calls) to satisfy the needs of the customers...However, Customer Service involves satisfying the needs of the customers using any form of communication. Email, Letter, Telephone or face to face meetings.

Usually their umbrella titles  for telemarketing, inquiries, support line and sales department calls.  Customer service agent can include on field sales.