Discover ducking responsibility

End of September I made an incorrect payment to a vendor in Botswana using my Discovery Credit card. The charge was reversed within an hour after engagement with the vendor. The original charge and the reversal was the same Pula amount. However, Discovery used two different exchange rate to convert in Rand leaving me short. I lodged a complaint and fter more than a month, they fianlly came back and told me that it was out their hands because it was government exchange control. This is the first time ever I have experienced this and I have had foreign charges reversed before without issues.