How to Create Case in Microsoft Dynamics CRM 2016 (Version 8) using webservices or REST API in JAVA or C#?

I want to create a case in Microsoft Dynamics 2018(Ver.8) using either C# or java using web services.After doing a vast googling I'm having hard luck with no or very few resources that are hardly useful. The Microsoft documentation is a complete dead end.Following are my requirements:

1. Creating a CASE.
2. Updating CASE more likely closing of CASE.
3. Creating a CONTACT.

I need to perform these actions using Rest API or Webservice either in JAVA or C#.Any help would be appreciated.