This will definitely work.
Latest Maven dependecy code is added to pom.xml https://mvnrepository.com/artifact/org.testng/testng
Download "TestNG for Eclipse" from Eclipse Marketplace
and Finally
Right-click on any file/folder in the project in Eclipse.
Select Build Path -> Configure Build Path.
Select 'Libraries' tab.
Click on 'Add Library'.
Select TestNG. Click 'Ok'.