Over changed!!!

Please to help me in this matter ,my electricity bills is four time the usual,I live by myself in equestria but get to pay more than what I believe I use, strange enough I made a payment on the 20th last month of R1500 from paying R400-500 and on the 11th this month I got an invoice saying I now owe R2800, how??? I don't know but I've realized my invoice now comes double in my statement and when I ask them they told me it's my usage .help me resolve this matter please