Exorbitant Voltano Bill

I am sooooo frustrated and not happy with the exorbitant bill of R4600 I received from Voltano last week. I stay in a 3 bed apartment with my kids who are normally at school during the day...I would switch geyser off in the morning and on in the evening and the fridge will be the only thing on. And with this I would normally pay around R2500...so last week I paid R2500 before receiving the statement to my surprised it was R4600. I immediately sent an email indicating my dissatisfaction of the exorbitant bill but I have not received any response because I sent it Friday evening. I called Voltano today Monday 25th Sept and I was told they are not responsible for my electricity usage but if I have been using my electricity a similar way and I know more or less the amount that I normally pay and I paid that amount but the bill was way way too much...please please assist.