IDB
You should certainly contact the Tribunal Service and the DWP about the report, however, as you have not suffered a breach of the Data Protection regulations, it is the person who's report has been sent that has suffered the breach, I don't see how you any complaint that you might make can extend beyond your report not being included.
I would contact your MP about the issue
Contacting your MP If there is contact information for the other claimant then you could contact them and make then aware of what has happened.
Gordon