I rented a car in August. Was in a hurry when I returned it (it was a small mountain airport station) and only opened the email receipt once I got through security. The charges were $420 higher than expected and it was clear that the core charges (daily/weekly rate) were higher than what was quoted which caused the difference. I emailed Hertz. No reply. Disputed with AMEX and was credited the funds (Based on the way that AMEX responded after a due waiting period, it would seem Hertz may not have responded to them). A few weeks ago, I received a statement in the mail showing the incorrect charge breakdown, the credit of what I did pay (after the dispute was factored in), and asking for $420. No cover letter or anything. I assume that if I just ignore it, Hertz will continue to pursue it? Thoughts on most effective way to deal with this?