Convergys Java Software Engineer interview questions

I applied through a staffing agency. I was interviewed in Convergys Manchester office after 1 round of Telephonic interview, which was pretty basic, getting to know my experience, my competencies, aspirations etc. On the day of F2F interview, there was a 2;1 technical round with lots of question ranging from OOPS basics to framework questions on Spring and some DB questions. The difficulty level was basic to intermediate. Thereafter a competency-based round with HR involving some questions around your professional past experiences about how you handled difficult situations etc. From what I perceived, all the rounds went well and they seemed happy, asked me about my expectations, notice etc before signing off. The staffing agency told on the same day that feedback is positive and they are going to make an offer. To my sheer disappointment, I never heard from them thereafter. I kept following up with agency who kept repeating that they don't have a clue whats going on and they are following up as well. Even if its a rejection, I believe its a courtesy to let the candidate know with a brief explanation of the reason instead of just no response whatsoever and keep them hanging. All in all very bad experience. Did not expect such unprofessional behavior from a big brand like them.