Almost 140,000 households across Norfolk and Waveney are still waiting to get their £150 council tax rebate.
And charities fear some older people could miss out completely, while some payments are still weeks away.
Councils have been paying the rebate, announced by chancellor Rishi Sunak to help combat the cost of living crisis, into accounts of households with monthly direct debits set up.
More than 280,000 households in Norfolk and Waveney have been paid a total of more than £42m.
But tens of thousands do not pay by direct debit, so councils have had to come up with mechanisms to ensure they get payments.
Some have had to divert staff to get new systems set up to allow rebates to be processed.
Thousands of letters are being sent to people informing them how they can give councils their banking details so they can get rebates.
Some councils have set up online forms so people not on direct debit can provide necessary information.
And some authorities have said, if the online forms are not filled in, £150 will automatically be credited to council tax accounts.
But a charity which represents older people fears inconsistency across councils - and a lack of alternatives to online forms - could mean some older people end up missing out.
Ellen Rasberry, information and advice manager at Age UK Norfolk, warned the use of online forms meant some older people risked being "digitally excluded".
She said: "Getting assistance with claiming benefits or rebates is becoming increasingly difficult for vulnerable older people.
"The difficulties many are facing exclude them from receiving timely financial support, as some find navigating the process too confusing and many don’t have access to online application routes.
“How the £150 energy rebate scheme works may differ, depending on your district council.
"All those who do not pay by direct debit will receive a letter informing them how to make the claim.
"The issue is that most districts in Norfolk are requesting this is completed online, digitally excluding the most vulnerable who cannot do this without assistance.
“All councils should include an offline option, so it’s important that you contact your local district council to request this.
"Some district councils will automatically credit your council tax bill if no claim is made, others may not so it’s important you seek information and advice from a reliable source."
She said Age UK Norfolk advisers could offer information and advice on how to do that via 0300 500 1217 or advice@ageuknorfolk.org.uk.
The government announced the rebate support earlier this year, with payments administered by local authorities for households in council tax bands A to D.
North Norfolk District Council, Breckland District Council, South Norfolk Council, Broadland District Council and East Suffolk Council already have online forms up and running.
Gail Harris, deputy leader of Labour-controlled Norwich City Council, said: "We do understand there are many people relying on the £150 council tax rebate to provide some support.
"While we have paid this to more than 30,000 households already, we are now working as quickly as we can to make sure that those who are eligible to receive this payment do so as soon as possible.
"We will be writing to each person we do not have bank account details for, with instructions for how they can give these to us securely, so we can get the money into their accounts.”
A spokeswoman for West Norfolk Council said: "Setting up the payment process has been complex, with lots of testing required to make sure people get the right amount as quickly as possible.
"We have allocated additional staffing resource to get these payments made as a priority and are pleased to be able to reassure people that the payments are now being received by residents and we are working through the remaining accounts as swiftly as we can."
She said the council's online application form will go live soon and paper forms will be available to those who need them.
A Great Yarmouth Borough Council spokesman said: "This is a new type of payment for local authorities and we are working with our software suppliers as quickly as we can to make the payments, while also making sure we follow anti-fraud requirements.
"We will contact everyone eligible directly during June, so please be patient if you haven’t heard from us yet."
Last month, the EDP launched its Your Money Matters campaign, to highlight the impact of increased financial pressures in the county.
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