overcharge and undercompensated

I made a booking for a holiday approximately 11 months before I was due to go. They charged me upfront 30% deposit and five months later I paid in 845 euro to reduce my final cost. 30 days before my holiday I got confirmation that I had outstanding 520 euros. Within days they deducted 1117 euros off my credit card instead of the 520. euro. Since then I have had major issue getting refund AND with two refunds I am now suffering variance n exchange rate. Credit card charge was at R16.46 per euro yet refunds I only got compensated at appr R15.20 per euro and have a negative of over R800.00 because of this difference in exchange rates. They not interested in my loss because of their error. Is there anything further that I can do as several emails to them and I am not getting satisfactory answers.