Complaint Review: Cabo Auto Sales

We bought a 2000 Mercedes Benz ML320 from Cabo Auto Sales for approx. 10K Cash - as we were signing the papers they advised us to pay them an additional $300,- for some sort of 'Premium Warranty/Assistance' since the car we were buying didn't come with any type of Warranty we agreed and paid them the requested $300,-.
We were told we'd have the paperwork in a couple of Days. 2 Days later Cabo Auto Sales contacts us and tells us that the Service they sold us on is all of a sudden 'no longer available' and should they go ahead and sign us up for a equal service/program, naive as I am I agreed...
Now it's 3 weeks later, I had to spend $2500,- on a new Transmission that magically broke soon after buying the Car, $1000,- on a Rental for that Time (We donated our old/2nd car to charity), got stuck and needed mechanical help on numerous occasions in numerous parking lots because the car just decides that something else is wrong with it...
All of this is fine, We read the 'Fine Print' and are/were aware of buying a car without warranty, but that these people after scamming us the way they did now pretend like we're crazy, ain't right!

Resolution Sought:
I'd like to pick up my $300,-, I've contacted them numerous times but only get the run around, here are a few of the Tings I've been told to date;
1) You already picked up the money
2) We never got the money(thank g for receipts)
3) You've waited too long, deposit 'expired'

Date Problem Started: 4/26/2010
Date of Transaction: 4/21/2010
Amount in Dispute: $300.00
Invoice Number: D5333
Complaint Type: Refund Promised
Product or Service: sells used/broken! cars and makes you pay for services not rendered