I rented a car in the US from Hertz while on a long trip there. I wasn't sure of the exact return date (several weeks) and I only had an international debit car

I rented a car in the US from Hertz while on a long trip there. I wasn't sure of the exact return date (several weeks) and I only had an international debit card and not a credit card. The guy at the counter was perfectly fine with this, said he'd note it on the file and I could settle up when returning it, whenever that was. Drove the car around the East Coast for weeks and then returned it and paid what I owed. Got back home to Australia and found threatening letters from them saying that the car hadn't been returned and was considered stolen, police had been notified, etc. The letter was sent at about the 10-14 day mark, and from memory we had the car for at least a few more weeks after that. Ignored it and never heard anything else about it. Whenever possible, I use Alamo when in the US. They've always been excellent.