Green Star Energy

I was Surprised that my bill for the first quarter was over £400 when I call up to ask why it was so high they said they would do a Re read to give me more accurate bill a couple days later I called back and was told I I had a further £256 more to pay 💰 when I asked to explain why the bill was so high I was told that they don’t have that information and that all I had to do was pay the outstanding bill when I asked for a team leader they said you’re just get the same answer from everybody else . I thought She was rude and intimidating I was told when I joined I would paying on an average of £75 a month. Which is clearly not the case. Can I switch back to previous supplier ?And do I have to pay this for £400 even though I believe I don’t really all this as I live by myself and don’t see how I could around up a bill each month of £100