Exorbitant Service Fee on Prepaid Electricity -FNB APP

I have bought prepaid electricity for R1000.00 using FNB app and was charged R109.00 service fee. According to the transaction details on the app, only R2.50 is charged on the transaction. To my surprise when I received the token via sms, it was written: FNB:-City of Ekurhuleni. Elec Amt: R759.78 Vat Amt: R130.44 Meter: 142******22. Units : 293.8kWh. Service Fee: R109.78.

This is daylight ******* as one can easily walk to a supermarket and buy without incurring such an exorbitant service fee. What is the R109.78 for