Hi Umang Kothari, thanks for the additional context. please use this quickstart to subscribe to delivery report events and troubleshoot. Once the events are configured, inspect the "deliveryStatus" field of your delivery report to verify delivery success/failure. Let us know if it provides additional information about this issue.
In the meantime, is it possible for you to send us message samples and message ids? We can try troubleshooting on our end. If yes, reach out to us at azcommunity@microsoft.com with the subject ATTN: Grace and in the body of the email. Also include your Azure Subscription ID and a link to this thread