Casa Systems Technical Support Engineer interview questions

I have interviewed several companies and this is the worst experience ever. First call from one team leader to ask some basic technical questions related to your Resume and potential job and invited to an On-site Interview. After that, The lack of management about the HR team shows up. I have been asked to same question from different person in HR team in EMAIL. They requested the previous pay stub of you after the on-site interview. The only purpose in my understand is to offer you as low as possible. Then I received an EMAIL to say that we are preparing an offer for but we need more information and material of you. I'v sent what they want and finally received an official refuse letter without any specific reason.