IntegriDATA C# Software Developer Fintech interview questions

First, I was given a take home coding test to write a program. After finished it, I was scheduled a WebEx interview. The guy gave me a bunch of codes which looks like a source file in their project. I concern if they use me as free worker to help them fix something. The interview went very unpleasant and most questions are tough, not commonly used or can be searched by Google.