Why has Zerodha not emailed the login credentials even after 3 days?

The email with the user ID may not have been sent for the following reasons:

• The account opening process is incomplete. Visit zerodha.com/open-account and complete the process. To learn how to open an account online, see How to open a Zerodha account online?
• The supporting documents are rejected. To learn the different rejection reasons, see Why was the account opening application put on hold? The rejection reasons are communicated with the client through email.

Once the account opening process is completed and verified, an email with the user ID will be sent within 72 working hours.