Meta Software Engineer interview questions

I had a phone interview where the interviewer asked me two programming questions. I answered both of them and some follow up questions. The recruiter said she will get back in two days. My interview took place on Tuesday and I sent a feedback immediately that it was good as I answered both questions in 45 mins. I did not get any reply till Friday. On Friday she said that she will call me on Monday 3pm regarding feedback. On Monday she called me and told me that unfortunately they are not going to continue the process with me. I was really surprised and asked about what went wrong and she refused to give me any more information. I am not sure on what grounds they rejected me. Not sure what else do they expect from an interviewee. I feel its totally unfair and have a very bad opinion about Facebook.