Advice Direct Scotland, which runs the national consumer and energy advice services consumeradvice.scot and energyadvice.scot, emphasised that it is vital that people check that they are receiving support.
Almost one in five households in Scotland use prepayment meters, but recent figures from energy regulator Ofgem suggests this is on the rise.
Vouchers worth £66 were sent out by post to prepayment meter customers from the start of October, as the first instalment of the Support Scheme.
Some consumers may have received an SMS text or email, depending on their supplier.
Most households will have £400 automatically taken off their electricity bills in six instalments across the winter. However, those on traditional prepayment meters need the vouchers to get the discount.
Payments of £67 in December, January, February and March will follow payments for October and November. Households with smart prepayment meters will be credited directly in the first week of each month.
The prepayment vouchers should arrive before the end of each month, but they are only valid for 90 days, with several suppliers stipulating they be redeemed at Post Offices while some can be used at other locations such as PayPoint shops.
Following reports that only around a third of vouchers have been cashed, Advice Direct Scotland wants to make sure that households do not miss out.
Colin Mathieson, Advice Direct Scotland spokesperson, said: “Suppliers may transfer customers to prepayment meters for several reasons, including issues with energy debt, with repayments being taken from arrears every time the customer tops up their meter.
“We would urge any households with a prepayment meter to check whether they have been sent a voucher and use it, and also to keep an eye out for the following vouchers. Consumers should already have received vouchers for October, if they have not they should contact their supplier.”