Mechanic Did NOT Fix Car! What do I do?

My boyfriend and I share a vehicle. We were supposed to be paying off our current vehicle last month, we only owe 1,000 dollars on it. We've had it for a little over a year, and we've never had any problems until recently. Last month, we took our car to a shop and received a diagnostic test. We found out we had car troubles, and we got our car from the shop. The same day, our car stopped working. So, we had our car towed to another shop. This shop had our car for a month! They kept saying they hadn't received the part to fix it. I was getting very upset. We need a car to survive, and this was very inconvenient. Long story short, we finally received our car yesterday. And, my boyfriend drove it to a gas station in the next town over. He wanted to test drive it. It stopped right away. It was only a 15-20 minute drive from our home. We had to get our battery charged, and then we made it home. I got up this morning, and the car would not start at all. We've had it for less than 24 hours, and it is already doing the same thing it was when we gave it to them. My boyfriend said that he called them, and they told us to call them today if it still wasn't working. And, of course, they are not open on Saturdays & Sundays. And, their voicemail box is full. So, you can't even leave a message. I want to go up there Monday and get my money refunded for the car. I don't even want them touching it anymore. The total price to have it fixed was $437 dollars. I am totally pissed, and I want my money back. I want to take it to a different shop, but I am not paying twice for a problem that was never solved in the first place. How should I go about this?