Electricity bill of R1200 for the month I wasn't living there anymore

I gave a month's notice letting them know I was moving house. I then got charged for the month after I had left. R1200 for no electricity use. While trying to sort this out I was passed from department to department, no one really helping me ever, until they sent me an email telling me to fill in a form so they could charge me extra cancellation fees. I refused, didn't sign or pay, and am now being threatened with legal action.