In the vast majority of circumstances, you can recover your credentials. E-mail is the most common method of retrieval. It may be possible to retrieve it either online or by calling a toll-free number. Check your spam folder for an email from the ICAI regarding your registration number. If you don't have it, contact the ICAI, send them an email, and they'll get back to you.
Hope this helps
Regular exam updates, QnA, Predictors, College Applications & E-books now on your Mobile