Prepaid electricity query

Just paid R1000.00 for 72 kw of prepaid power through Fyfhoek Spar Store. Previously and recently this same store gave us 322Kw for the same amount. The slips are kept for recording purposes. On the account slip an amount for R877.78 is included as partial block. When this was queried with the management. They actual charged us R20 more for the query and fobbed him off. I tried to contact spar management but only got through to a wharehouse. If this is where Spar Fyfhoek Potchefstroom is headed I would advise avoiding them. However if this is s mistake I am sure they would want to correct it on our second attempt.