Sir,
According to Rule 2 (f) of POP Rules, 2012“intermediary" means a broker, an agent or any other person, by whatever name called, who arranges or facilitates a provision of a service (hereinafter called the 'main' service) or a supply of goods, between two or more persons, but does not include a person who provides the main service or supplies the goods on his account."
According to Rule 9 of POP Rules, 2012 the place of provision of intermediary services shall be the location of the service provider. In your case the intermediary service is provided by 'C' who is located in India (taxable territory). Since the intermediary service provider is located in taxable territory 'C' is liable to pay service tax.