2276,60 Euro Car rental Bill years later

If the bill is for a car rented more than 4. ( four) years ago, then the California Statute of limitations has expired and there’s no way the agency can enforce it. Do not communicate with the agency as this may restart the Statute of limitations. Instead, contact your bank that issued the credit card it’s presumably being charged to, and let the bank deal with it. If there is no credit card involved, then this appears to be a scam. Your bank can require the car rental agency to produce proof this was actually rented by you ( if it’s less than 4 years ago) and if damage to the vehicle is alleged, they can ask for documentation. Unpaid accounts that are neglected for years simply cannot legally be collected on.
There are stories out there of fraudulent schemes regarding car rentals. This could also be that type of scenario. The odd thing about your story is that any legitimate car rental agency would already have billed your credit card. That’s why it smells scammy.

It is just a bill, not a charge to your credit card. It sounds like a scam. Do they want want you to send the money in gift cards?

Wow!!! Without an explanation of the nature of the charge, especially if you haven’t done a Sixt rental in the past 2 (or 3?) years, this sounds unworthy of any concern. If they had your credit card number, which sounds like they don’t (any legitimate rental company would have the card number you used for your rental), and had charged it, then you’d just contact the credit card company to dispute/refuse/reverse the transaction. If no charge to your card, there’s nothing they have done (or can do) to collect money without your consent,

I wonder how the sender got your mailing address? And in this day and age, why wasn’t it done via e-mail? But showing up in your mailbox, without an itemized invoice for the charges, especially from a top-end rental company like Sixt? Unless they can provide further details as to the alleged infraction, this is one to ignore.

If it’s legitimate, they can follow up with more supporting documentation. Regardless, they have to go out of their way to get money from you, wrong or right, so they need to be clear about why they’re billing you, as if they can collect the money without your cooperation.

… Or it’s a scam, from someone who was able to reach you, through your mailbox.

Riverty is a German based Financial Services Company which, among other services, such as invoicing, bill payment platform methods, also has Debt Collection Division. They are present with offices in several countries, including Seattle WA.

Assuming someone used Sixt or some other rental company which uses Riverty for their debt collection, this sounds like a bill for some damage done to the rental car after returning it. The rental company is probably using Riverty for collecting that bill.

I wouldn't worry about it unless they charged your credit card already, in which case you should dispute it with your credit card, as suggested by the comment above.

If a collection agency starts to pester you, I gave advice below on how to deal with it.

https://community.ricksteves.com/travel-forum/italy/paying-a-fine-from-the-us

If you didn't rent a/the car, don't pay it.

Is it a 'bill/invoice' that they are trying to get you to pay, or has that amount been charged to one of your credit cards?

How do they want you to make payment?

I would send then a request ( at wherever they want payment sent) for a copy of the rental agreement you are alleged to have executed.

I would try to find out whether this was originally send from Riverty Services GmbH by using their contact website.
The link from the middle box reaches a page which seems to be under maintenance (right now).

There was no charge to our credit cards. I forgot that hubby did rent a car last September in Germany from Avis.

The invoice is telling us the amount we owe will be increasing if we don't pay it. It has our address and name correctly, and written in English but no explanation of anything except small print in German. They have a bar code thing on the paperwork that takes us to their website were we are then given choices of how we want to pay the invoice.

We did email them asking for an explanation why they sent us the invoice. Hope that was ok! UGH!!!