Legally speaking there is no necessity for the Darul Qaza or the Jamaat to certify the Khulanama, because they are not the legal authority to grant divorce under Muslim personal law.
The Personal law is very clear that the khulanama or talaq becomes valid with anyone witnessing it.
If you still insist on further legal compliance in this regard, you may have to file a civil suit for declaration to declare the dissolution of your marriage by Khulanama is valid.
No doubt this divorce decree/judgment would be pertinent if you want to remove your spouse name from your passport and not otherwise.
Therefore this Khulanama declaration with two witnesses attesting the same is a legally valid divorce as per Muslim personal law in general law too.