I just heard back from CashCase. They say:

"If you are making a purchase in a currency not supported by your card, for example the rand, your card will look to draw funds from your British Pounds purse and the exchange rate applied will be the prevailing Visa exchange rate plus a 2% international transaction fee will apply."

Kind regards

Olly, your editor

I've emailed CashCase to ask for you but haven't heard back yet. I'll let you know when I hear.

If you would like to contact them yourself, their details are:

email - help@mycashcase.co.uk

freephone - 0800 756 7723

Kind regards,

Olly, your editor