I recently rented a car with Sixt through Auto Europe near Lisbon. 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. I was only expecting charges for the transponder ($17) and tolls ($20).

The extras were for optional insurance. Sixt and Auto Europe said that I signed the agreement and was therefore liable for this amount. I called the customer service department at Sixt because I felt I had been wrongly charged this amount. Sixt agreed to review my complaint and reply to me 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 to this statement.

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

Can you help me get my money back? — David Degagne, Angus, Ontario

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 an extra $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 like upgrades and insurance — there was a misunderstanding.

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

Initially, I thought there might have been a language barrier, although many people in Portugal speak excellent English. But you say the representative had a good command of the English language. 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 assures you that it’s what you discussed, and you sign it without realizing that you’ve agreed to pay more. It’s hard to know, since I wasn’t there.

It looks like you tried to reach out to both companies to appeal this decision. Remember, I publish the names, numbers and email addresses of the executives at both Auto Europe and Sixt on my consumer advocacy site, Elliott.org. A brief email to one of them might have reversed these charges.

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 and telling you what’s in it. That’s where problems happen.

Still, I think there was a misunderstanding, if not some deception, involved in your rental and I wanted to give Sixt a chance to review it. So I did.

“First of all, we would like to apologize — also on behalf of our franchise partner in Portugal — 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 charges.

You told me you are happy with this resolution. “I hope this serves as a reminder to your other readers to make sure that they fully review their contract before driving their car rental out of the garage,” you added.

Christopher Elliott is the founder of Elliott Advocacy, a nonprofit organization that helps consumers solve their problems. Email him at chris@elliott.org or get help by contacting him on his site.