Please help with Sams club.?

I took my BMW M3 to Sam's Club to change the tires. The next day I was driving and the rear driver side wheel almost came off the car leaving one lug nut to hold the wheelon. My car was swaying like crazy all over the road. My rim was destroyed so I sent them an estimate for $5400. Today I got a check for $4500. I contacted them and they continued to make excuses. The last comment made by them was if we don't receive a estimate from the BMW garage about your car then were not paying for your rental at $71 a day or the cost to fix your car. What the hell do I do?