If your certificates are lost or damaged, you can order duplicate copies. There are procedures in place if they are lost, such as a paper ad or a non-traceable certificate from the police. You cannot apply for duplicate certificates when the originals are available (available on the website).
You can ask the management for the certificate's return or file a police report against the college if it refuses.
Getting a duplicate certificate of your mark sheet from Anna University is now very easy. Here are the steps you need to follow:
Earlier you needed to file a police complaint regarding the loss of your original documents. Nowadays you do not need to do that.