More than one million households did not redeem their energy discount vouchers this month, worrying figures show.
The vouchers are being issued to prepayment customers as part of the Energy Bills Support Scheme (EBSS).
The cash discount is worth £400 in total but is being split into six months. Households should have received in October and November, then £67 in December through to March.
But new figures obtained by the BBC show only 27% of vouchers for December had been redeemed at PayPoint stores by 18 December.
It comes during a month where temperatures fell to below -15C and snow blanketed parts of the UK.
PayPoint said strike action by the Royal Mail might have delayed some vouchers being sent by post.
Steve O'Neill, director of corporate affairs at PayPoint, told the BBC: "December vouchers issued by email have already seen high levels of redemption, though December postal voucher redemptions are lower than we would expect, which could be linked to strike action in the UK causing delayed delivery.”
PayPoint figures show 73% of vouchers were cashed in last month, and 80% were redeemed in October.
Around two million energy customers on prepayment meters are receiving vouchers, which can be redeemed at the Post Office or through PayPoint.
Vouchers can be sent by post or through email or text message.
They are only valid for 90 days - so households who have received them are being advised to redeem them before they run out.
Direct debit customers should be receiving their energy bill discount automatically - meaning you don't need to do anything to get the money off.
The cash will be applied either as a deduction to your monthly direct debit, or as a refund to your bank account after your direct debit has been taken.
If you don't pay by direct debit, the discount will be applied as a credit to your energy account each month.
The credit should appear as if you'd made a payment to your energy bill.
Smart prepayment meter customers will also receive the discount automatically each month.
The £400 discount doesn't need to be paid back.
Your energy supplier won't need to ask for your bank details to apply the discount - so be aware of scammers trying to contact you.
What do I do if I still haven't received any rebate?
If you pay by direct debit and did not receive a rebate in October contact your energy company as soon as possible.
The same applies if you have a traditional prepayment meter and haven't received your first voucher.
It's worth checking your text messages, email and post to make sure it's not gone where you didn't expect it to.
