Dutch to English Bus/Financial Insurance vehicle insurance

Can anyone give me a good English translation of "aanhangsel van schuldvordering". Source text from Belgium. I believe that this same document is known as "avenant de creance" in French. It is basically a signed statement from an insurance company to say that the vehicle is covered for civil liability, legal assistance and breakdown. It is an attachment to a leasing agreement under which a company is leasing vehicles to Hertz for its hire fleet. The vehicle owners require this document to be attached to the lease agreement.

Here is an explanation I found online, though in this case the insurer is signing to say that comprehensive cover is provided:

"Behoudt u uw vaste verzekeraar? Dan ontvangt u van ons "een aanhangsel van schuldvordering". Uw verzekeraar vult dit in en ondertekent het. Zo neemt hij de burgelijke aansprakelijkheid, rechtsbijstand en volledige omnium op zich. Wij vogen het bij uw contract"