Seven people in ten pay their energy bills using direct debit, and every one of them needs to take action this week to stop overpaying.
And this isn't something you can put off, with MoneySavingExpert.com founder Martin Lewis telling people they need to act fast to get their cash back.
"The timing is crucial," Martin wrote in the weekly MoneySavingExpert newsletter .
"If you're one of about 70% who pay for electricity or gas bills by direct debit, check NOW if you're due credit back."
And you could be due a lot, with one reader saying they got £570 back after putting a call in.
Why now is the perfect time
Your energy use fluctuates over the year, with the heating and lights on more over the colder, darker months than over the summer.
That means people who pay the same each month build up credit on their account over the summer, that is then used over the winter.
But with winter now over, and summer not fully begun, your balance should be 0 if everything has worked out.
If it's not, and there's money there, that means you're overpaying for no good reason and it's time to get that spare cash back.
"To be a month's worth in credit right now is a lot, so unless you're with one of the few firms that pay you interest on it, politely request your provider explains why, and if its reason isn't good enough, ask for the cash back," Martin wrote.
Asking for the cash back
The good news is that when you're asking for the money back, the law is on your side.
"Condition 27 of energy suppliers' licences is that they must take reasonable steps to ensure direct debit levels are fair, and to explain the level they're set at," Martin explained in his guide to getting your money back .
"So call up and ask – there may be a justifiable reason."
If they don't have a good reason, the money needs to be refunded.
If you don't agree with their reason, you can also complain - free site Resolver can help you with this , and if that fails too you can escalate to the Energy Ombudsman .
Although there is one exception.
"If you're with one of the very few energy firms that pay decent interest on any credit, such as Ovo's 3%+, it could be an advantage to keep it there as that's more than you can earn in savings if you have no debts to clear," Martin said.
