Credit card/ Exchange rate.

My husband is working in Mauritius so after saving for a while we were still short of a certain amount so app**** for a Nedbank Credit card. I received the card and once again informed them i would only be using it for our Mauritius trip. We booked into a hotel which with the exchange rate should have cost us approximately R45 000. Only to be charged R65 000. After quering this with Nedbank we were told its the hotel that charged us incorrectly. After numerous calls to the hotel and the hotels bank they came to the conclusion it was Nedbanks issue (after having spoken to Nedbank on numerous occassions and them stating it was the Hotels issue). After numerous phone calls to Nedbank and after speaking to many different people i eventually get an email from Nedbank stating that they charged me 1.6 % exchange rate although the exchange rate was 2.4 at the time. Apparently they can charge any exchange rate they see fit. I am absolutely flabagasted that a bank can make R20 000 profit from me when i have only spent R45 000. Of course i am now financially unable to cover this credit card as this was totally unexpected. Not on any occassion was i informed of this. I get no fruther response.