Mystery charge and no response

I am a partner in a film company in Chile and we hire cars and trucks often. On a recent visit to SA I decided to use Europcar for a 47 day hire. All was fine and the bill settled in full 6 October 2017. Two months later I notice a charge on my foreign card in US dollars. Since then I have asked repeatedly for an explanation to no avail. I have 7 case numbers and 5 different names in 4 countries and still no response beyond 'we are looking into it'. My bank has put the charge through, and charged me the forex commission, and I still have no clue what the charge was for!