To my knowledge service is a layer where business logic gets processed (synchronously or asynchronously) whereas an endpoint is that same service exposed as a web-service whether SOAP based or Restful based.
Please correct me..
An association between a binding and a network address, specified by a URI, that may be used to communicate with an instance of a service. An end point indicates a specific location for accessing a service using a specific protocol and data format. [WSD Reqs]
It defines service as -
1. A service is an abstract resource that represents a capability of performing tasks that form a coherent functionality from the point of view of providers entities and requesters entities. To be used, a service must be realized by a concrete provider agent.
2. WSDL service: A collection of end points. [WSD Reqs]
3. See Web service.