Typically, your bank or UPI service provider will notify you via SMS/email once the mandate has been successfully created, and the corresponding amount has been blocked. 

If the shares are not allotted, the blocked amount is typically released within 10 working days from the refund initiation date or upon the expiration of your mandate. To check the mandate's expiration, log in to the UPI app where you authorized the mandate.

Here is the illustration to understand mandate expiry date (on GPay):

In case you don’t get any communication regarding the amount being blocked/released, kindly raise a request with your Bank.

Note: The bank account used to block IPO funds will be the one where the mandate refund amount (if applicable) will be reflected. Hence, ensure to check only this bank account for the mandate refund amount.