Charges for services not rendered.

Rented a vehicle from this rental company Dec/Jan. Did not provide them with a request for a second driver nor did they take details of a second driver. After returning from holiday found charges for a second driver. Responded to their email to the address listed in the body of their email and to date no response. Absolutely pathetic that they cannot provide a response still two months later. If they can add charges on like this, then how many unsuspecting customers do not look at their invoice?