I have just received my gas and electric bill from scottish power,?

And it has gone up from march, over a thousand pounds, I live in a small 2 bedroom house, i hardly have the heating on, but there saying i have used more gas, i do not have a gas cooker, all i have is my boiler, the only thing i have on quite a lot is my tower fan because of this hot weather, I had a electrician come out at christmas to install my cooker, and he said a lot of the wiring i have is quite old fashioned, could this have influenced my bill?