Hii!

You haven't mentioned the name of the University or College you are talking about. But, you must have got a message or email when you registered yourself for the exam. Search for it. If you get it, you will get your hall ticket number in that.

If that's not the case, you may inform this to the office of your College and ask them for help. They may help you find it or provide you with the duplicate copy.

Hope this helps.

Good luck!