many questions were asked during 40 minutes interview, some questions were tricky like what challenges u think u will have once you get this job and how would u deal with that

I was interviewed on 11 January 2019 , I received offer letter on 15 January and just before joining 24-48 (hrs) I was told about this discrepancy. I with my whole family was in total state of shock. I could not understand , why it took so many days for you & your organization to notice this discrepancy, I would have happily accepted if it had come within 2-3 days after interview & scrutinizing my credentials. But this incident make it look like you are purposefully playing with my career, as I had resigned after your confirmation of joining. May be it will not cause any major effect but certainly it will create a ripple about your HR policies .  Although I have suffered a major blow but hopefully other candidates will take full precaution before entering your so called esteemed organisation.