I've actually had fairly good experiences calling Heartz on the phone. Did you pay for the reservation ahead of time? If you didn't, then there's no need to can

I've actually had fairly good experiences calling Heartz on the phone. Did you pay for the reservation ahead of time? If you didn't, then there's no need to cancel it. If you don't pick up the car your credit card doesn't get charged (at least with Hertz). I usually call and tell them I'm canceling the reservation out of courtesy, but even if you forget, if you don't pick up your car, the reservation is invalidated. I also once showed up 4 or 5 hours late at Hertz, and they told me they'd cancelled my reservation since I didn't show up. I think they said they only hold it for an hour from the reservation time. I believe Hertz also lets you cancel your reservation online if it's more than 24 hours in the future. So you'd only need to call if it's <24 hours in the future.