Eccessive Service Fees on Prepaid Electricity.

I purchased R350 prepaid electricity and i am charged a service fee of R248.50. So in essence i am only getting R101.50's Electricity value. I have done this 3 times now in the last 2 weeks on 3 separate occasions purchased the same amount and the service is the same. This is ridiculous. Why are your service Fees so high and what is the service fee for? On previous occasions when i purchased Prepaid electricity from you there were no Service Fee charges. How can you take more than 70% of the value of the Electricity topup?