Generally, your bank/UPI service provider will send you an SMS/email when the mandate has been created successfully and the amount has been blocked.
If the shares are not allotted, the blocked amount is released within 10 working days from the refund initiation date or on the expiry of your mandate. To check the expiry of your mandate, login to the UPI app from where you have 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.