https://en.wikipedia.org/wiki/XGI_Technology
If someone sold you this card as "New" and using an "ATI" chipset, they were not truthful with you.
In the interim I looked at the NetBSD kernel configuration. In the default kernel the mga driver is turned off. It may be possible for you to utilize the matrox card in NetBSD. You would have to build a custom kernel which is not an easy undertaking.