Tarrifs not adding up.... Not making sense.... PLEASE ADVISE

I am battling to understand the following: Every month I buy the same amount for electricity. This is a breakdown: 2023-09-26 | R300 inc Vat | R260,87 Total Excl Vat | Total Units: 130,4 2023-10-29 | R300 inc Vat | R260,87 Total Excl Vat | Total Units: ***-11-25 | R300 inc Vat | R260,87 Total Excl Vat | Total Units: 95.10 2023-12-23 | R300 inc Vat | R260,87 Total Excl Vat | Total Units: 95.10 2024-01-29 | R300 inc Vat | R260,87 Total Excl Vat | Total Units: 91.50

Please advise how it is possible that we receive less units nearly every month while paying the same amount. If my knowledge is correct, there was not a tariff increase yet from eskom, yet, we experience a decline of units from 130 units to 91.5 units in a 5 month time frame? That is a drop of 38,9 units within 5 months. How can that be possible.