Vehicle insurance when out of warranty

I have a 2015 polo, which was ****** and recovered in 2021, the radio was replaced but it wasn't the original vw radio. when I asked the insurance company why was the original radio fit, they said the are not obligated to fit a new original radio because the vehicle is out of warranty. Is this true, if so why do the not reduce the installments when the vehicle goes out of warranty because I'm paying for an original part but I'm getting a second hand or after market part. This is not fair and not right.