Eon customers are furious after the energy firm sent them pairs of socks as bills sky rocket.
The supplier says the ploy was done to encourage households to turn their heating down and help reduce their carbon footprint.
Energy prices are due to soar by £2,000 in April, among the rise in the cost of living, with many families worried how they will cope.
Customers took to social media to slam the company's efforts.
Competitor Ovo Energy similarly found itself in hot water earlier this week by suggesting customers have "a cuddle with pets", as well as eat bowls of porridge and do star jumps to keep warm.
It later apologised, admitting it was a "poorly judged" move.
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Deano Hazell wrote on Twitter : "What is the point of sending out one pair of socks to keep warm! Would be better reducing bills that are going sky high instead of spending money on what I think is poor taste and a waste of money."
Sarah Collins said: "My elderly auntie on income support just received this pitiful package from her energy company!!
"A packet of polyester socks. Are they for real?? As if suggesting cuddling your pets wasn’t bad enough? Shame on you E-On."
Marge Newbs said: "Received mine this morning. Hubby and I going to have one each. What a joke, are they telling us electric going to be so expensive we will have to forgo heating our house?"
Kirsty Gleeson questioned: "What is the carbon foot print for the manufacturing and distribution of these socks?"
Age UK said in a statement: "The unprecedented hike in wholesale energy prices will be totally unmanageable for those living on low fixed incomes – many of whom have few, if any, savings to fall back on.
"Many older people are already putting their health at risk by rationing their food and heating to keep their bills down."
It went on to say many older people are "too worried" to use the oven and so are living on soup and sandwiches, while only showering every couple of days and turning the heating off part way through the day.
Referring to the Eon sock gesture, Martyn James, of complaints site Resolver, told the Daily Mail: "Even with the best intentions, this type of marketing stunt will feel like a slap in the face to households panicked about the soaring cost of energy.
"It’s also a complete waste of money that could surely be put to better use given the current crisis."
Eon has confirmed it sent around 3,000 customers socks as part of an energy saving campaign.
A spokesman said: “This activity was in no way designed to detract from the seriousness of the current energy crisis and the work we are doing to lessen its impact on our customers and we’re incredibly sorry for how we have made some of our customers feel.
"This campaign originally went ahead last year and was intended as a fun way to encourage people to think about ‘lightening your carbon footprint’ and isn’t meant to be anything to do with the current challenges many people are facing.
"To help our customers E.ON has invested billions of pounds and helped millions of people around the country to improve their homes.
"That includes better insulation and more efficient heating and it also involves simpler things like providing help and advice to customers so they can use less energy in their everyday lives.”
