Hi Navs11,
sorry to hear that your application was returned. So unfortunate. They could have atleast asked you to send the proof of marriage again.
In our case, we anticipated the issue after we had submitted the application. But some people mentioned in the forum that they cleared the entire process without any questions asked. Anyway, they put a hold to our application and asked us to submit the marriage certificate within 60 days. But IRCC did acknowledge that a true extract was received but they still needed a marriage certificate to continue.
During our marriage registration, we asked the registrar and he confirmed that the 6 page extract is the only proof provided to anyone who registered under the Hindu Marriage Act. But we still approached the registrar's office (after IRCCs reply), whether they can provide a marriage certificate. They clearly said a NO. The only option they could give was to redo the registration under Tamil Nadu Marriage Act with both of us present and get the marriage certificate after 30 days. So, we did the following.
1. We got a letter from the marriage registrar stating "the true extract is the only proof of marriage offered under Hindu Marriage Act" (with both the seals - registrar's and TN Govt's round seal)
2. Created a short manual on how to verify marriages on tnreginet website. Literally pasted screenshots and made a PDF, that the IRCC officer can easily follow and verify.
3. Wrote a cover letter explaining the whole issue.
4. We filed 2 RTIs - one to the concerned registrar's office and one to the IG of Registration. We did get reply from both the offices but it took too long that we submitted before the replies arrived.
We submitted 1, 2 and 3. Our document was accepted the same week and the issue was solved. I will suggest the same for you. I strongly recommend including RTI reply (although we didn't do, due to the time constraints)
Note on RTIs: Most of time, they only give you Yes or No response to your questions. So, make the question you ask on RTI is very precise and clear.