Fuel poverty charity Energy Action Scotland said it was expecting an additional 250,000 households in Scotland to receive the broader Warm Home Discount payment this winter.
Households need to be receiving a means-tested benefit such as Housing Benefit or Universal Credit.
Suppliers then check eligibility with the Department for Work and Pensions or Social Security Scotland.
Frazer Scott, chief executive at Energy Action Scotland, said he found the situation in Govan “incredible”.
“It’s absolutely ridiculous that, for a company with the resources that Scottish Gas has, they cannot get this right.
“It should have been sorted a long time ago.”
He added: “I cannot understand why it is left to the eligible person, someone who is in need of financial support and someone who is likely in difficult circumstances, that they have to try and come up with a fix for this when it should be energy supplier moving heaven and earth to help these people.
“There is a huge question mark about people’s ability to engage when many of the only routes companies seem to have available these days are electronic or web-based.
“Companies are not working hard enough to support all their customers fairly. People should be at the heart of the system, not processes.”