Help: D&M Motorsport Chicago rip off

[38talon]

Hi together
My name is Steffen and I'am from Germany. I seek the help of this forum now because i made a very bad experience with D&M Motorsport in Glenn Ellyn / Chicago. Their website is www.dmautosales.com
I bought a Superformance Cobra from them last year in Mai. Part of the deal was that they put shoulder harnesses in the car. First thing is that they told me to forgot to put the belts in the car and told me to send it. Until NOW i dont have the seatbelts. Second and worst thing is that the car arrived here in Germany with a bad cylinder head gasket. My shop here had to pull the whole engine to change it because of the bolt size and the fact that its a big block. Very expensive thing to do. There was also one of the bolts from the driveshaft missing and the others were loose. This could have lead to a major accident. The car had also a front damage which was professionally repaired but never told to me.
I called D&M the last year I guess more than 50 times but there is no reaction from them. I have the feeling that they just want to make money and as soon you payed they dont care anymore.
Has anyone made similar experiences with this company?
What should I do now?

Thanks Steffen