Mom and I

I’m having a kinda huge problem, my husband and I bought a new truck a few months back. Though since that day my mother has said that my old car is hers... and it’s a argument we’d always have since I paid for that car when I was younger, and well my husband and I are having problems getting to each other since he works out of town since we only share the truck since according to my mom my old car is hers. I wanna ask for it back but how? How do I say it without sounding rude??