Electricity units dropping

Can someone please explain the drop in the amount of units when buying electricity 3 times in a space of a week ? For R200 on the 24 Jan 2021 I was getting 83.4 units kWh For R200 on the 28 Jan 2021 I was getting 71.4 units kWh and today 31 Jan 2021 I am getting 68.6 units kWh for R200.