How is the refund exchange rate 7 points higher than the date of sale rate?

[CXXVI]

I made a purchase worth $355 on November 22nd, the dollar rate was KES 129.5 to the dollar, but was charged KES 135 to the dollar. Yesterday I received a refund on the same transaction and the exchange rate was KES 128.7 to the dollar. I understand differences in the rates but a KES 7 difference while the currency has been stable makes no sense since the fluctuation is just KES 1. 

[kernowlass]

@CXXVI 

https://www.paypal.com/uk/cshelp/article/where-can-i-find-paypals-currency-calculator-and-exchange-r...