The consumer group says the discounted deals should be promoted more widely on social media channels.
Broadband providers need to do more to promote their social tariffs for low-income customers, with millions still missing out on vital savings, the consumer group Which? has said.
The consumer champion said its own research suggested providers are not advertising their cheaper offers on social media regularly.
Social tariffs are special discounted deals available to certain low-income customers – for example, those receiving Universal Credit – to ensure they are able to stay connected.
Which? checked the Facebook, Twitter and Instagram accounts for seven broadband providers throughout the month of May, but found only one provider had mentioned social tariffs in posts during that period.
It said its own research had found that customers who are eligible for social tariffs could save an average of £250 a year by switching to the cheapest social tariff.
A number of broadband operators offer social tariff discounts, but regulator Ofcom has previously noted that most people who are eligible for such deals had not signed up.
In February, it said that only 55,000 out of an estimated 4.2 million eligible households were signed up for the discounted deals.
The regulator called on providers to do more to promote social tariffs, make information about them clearer and ensure the sign-up process was as easy as possible.
“It is unacceptable that broadband providers aren’t doing more to make customers aware of social tariffs – meaning millions of households who may be struggling to make ends meet could be missing out on hundreds of pounds of savings,” Which? director of policy and advocacy, Rocio Concha, said.
“During a cost of living crisis, broadband providers must support the most financially vulnerable by clearly promoting discounted deals and making it easy for eligible customers to switch over to social tariffs.”