The problem they had given was not a great and complex problem. I had given a solution following the SOLID principles and Object Oriented concepts properly which is highly extensible. But I think the interviewer was expecting a simple and straight forward solution which any layman can design and the solution which I had given had gone over her head. She was not able to understand the complexity of the design whhich I have made. She had given me some more requirements to extend the design which I could easily incorporate in the solution which I had given as my solution was following all the standards of SOLID. But still she did not like the solution and argued with me about some base less points and still I was able to overcome all her arguements.