Cannot get support to resolve overcharges on credit card

I rented a car from Hertz for 6 days in late December 2018. The car was fine and the initial service I received was also sound. However, after returning the car I received a bill that had obvious errors on it, most notably charges for a large number of supplementary chargeable kms that I hadn’t driven. The full value of the invoice was promptly deducted from my credit card and I have been struggling for a full month to get this addressed and the overcharges refunded to me. I have sent emails on 4 separate occasions to the Customer Relations email address specified for invoice disputes on the Hertz website to request a review on my case. Furthermore I have contacted the Customer Care hotline twice to attempt to get help telephonically. In all cases, I get an initial contact going but no feedback that any follow up action is happening.