Q: I rented a car with Sixt through Auto Europe near Lisbon, Portugal. A few days after I returned the car, I received a charge on my credit card for an extra $513. I was shocked by the amount.

The extras were for optional insurance. Sixt and Auto Europe said that I signed the agreement and was liable for this amount. I called the customer service department at Sixt. Sixt agreed to review my complaint and reply by email.

Today, I received the same response stating "the extras were presented at the counter" and that I signed the document, indicating my agreement.

No one advised me of the optional insurance. If I had wanted it when ordering the car online, I would have paid for it. I specifically opted out of the insurance when I made my reservation.

Can you help me get my money back?

A: Sixt should have explained what you were signing when you arrived in Lisbon. And although it looks like both Sixt and Auto Europe have signed contracts in which you agree to pay $513 for insurance, I believe you never intended to accept the extra coverage. In fact, you said a representative offered you insurance for $50, which you turned down.

What happened? In reviewing the correspondence between you, Auto Europe and Sixt, it appears you initially declined the coverage online. However, at the counter — where agents are trained to upsell you on extras — there was a misunderstanding.

According to Sixt, the agent offered you optional insurance. Sixt says you accepted it and signed a contract. You say that you never did say yes to the pricey coverage.

Initially, I thought there might have been a language barrier, but you say the representative had a good command of English. This feels more like a variation of the "sign here" scam, where a car rental agent scrolls through a lot of pages that you can't possibly read, and you sign without realizing that you've agreed to pay more.

Let's be clear: If you signed something, you're responsible for it. And you should always read the entire contract before you sign it, even if someone is standing in front of you telling you what's in it.

Still, I think there was a misunderstanding, if not deception, involved and I wanted to give Sixt a chance to review it.

"First of all, we would like to apologize ... for the inconvenience caused," a representative told me. "We regret that David Degagne had a negative experience with Sixt and have reviewed the case with our local colleagues in detail."

As a "gesture of goodwill," Sixt reversed your insurance charge.

Christopher Elliott is the founder of Elliott Advocacy, a nonprofit organization. Contact him at chris@elliott.org or elliottadvocacy.org/help.