Not that. Newish 3 bed semi and we pay in the region of £30/month each for gas & elec. Get onto them, were you in debit to them on your last bill?
I had a problem like this a couple of years ago, they'd underestimated my bill, so when they got a reading suddenly we were miles behind, so they just lumped the monthly DD up massively to get the money back over 3 months.
This time last year I had to ring as we were 00's in credit, and take the spod on the phone through how to work out a monthly amount.
Me: "In £s, how much have we used in the last 12 months?"
Them: "£xxxs"
Me "Ok, so divide £xxx by 12 & that is my monthly payment, that should work out OK.
Them "That's not how it works, take £xxx and divide by 6, then add £15 per month, you'll never be out of credit again….."
😈
Get the company to explain how they've come to that figure, most customer service bods won't have aclue.
Just another thought, you've not just come off a fixed tarrif have you?