Sixt Car renta Munich Germany

This is a true car rental horror story

i rented a BMW 328i from sixt in Munich in 2010. I rented online at sixt.com. I used my credit card and availed of its rental car coverage feature and declined the CDW coverage online. The rental came to about €380. When I showed up in Munich to collect the car, I was given a form in German to fill out. I couldn't understand it of course, but the bottom had a €380 line item, so I thought I was simply signing fort he rental. The unhelpful customer service rep at munich airport assured me it was the standard rental agreement and I should just sign it. 

It turned out sixt had made a mistake on the order and booked me for CDW coverage. The amount came to roughly the same €380 as the rental. When I got back to America, I got a shock when my credit card bill arrived and there was a double charge on it. I called sixt and they refused to reverse it, even after I sent them a copy of my emailed receipt showing I had declined the CDW.

i then called American Express and disputed the charge. They gave me my money back.

i considered the matter closed.

i rented from sixt again on two more occasions in Europe with no issues.

Then in 2013, something amazing happened. I rented from sixt in Sweden, again booking through sixt.com. They accepted my credit card, gave me a reservation confirmation. Then I flew to Sweden and got off the airplane only to find the rep at the counter refused to rent me the car, stating I was blocked.

even worse, they refused to refund my money, telling me they were applying the funds to my "outstanding balance" 

Do not rent from sixt, at least in Europe. Choose Avis or hertz, they have never let me down.