Alternative Part policy that nobody is aware of or accepted.

I have logged a claim for my vehicle windscreen replacement. Outsurance then authorized the claim and Glassfit was sent to replace the windscreen. They arrived with a alternative part to be installed and not an OEM. I did not accept this as the item is not the same as what is installed. Outsurance Claims department then informed me because my vehicle was older than 5 years their claims policy states that they will only use alternative parts. Nowhere was I ever informed of this or accepted it. The installation of alternative parts will devalue my vehicle when it comes to selling it as well as having an impact on any warranty claims if such should arise.