Council tax bills wrongly showing, in some cases, a freeze-busting 17% increase have been posted to tens of thousands of homes in Devon.
The blunder by two Tory-controlled district councils Torridge and Mid Devon, this week saw more than 60,000 bills posted out.
The mistake has prompted calls for the resignation of those alleged to be responsible.
Des Hannon, the Liberal Democrat opposition leader at Devon County Council, who received one of the incorrect demands at his home in Tiverton, said Mid Devon's cabinet member for finance, Neal Davey, should resign
Mr Hannon, who is set to stand against Mr Davey in the upcoming county council election, claimed the postage costs of the Mid Devon batch alone was estimated to be more than £12,000
That is claimed to be a figure which could have kept a tourist information centre open for three years or prevented a move to limit sandbags.
"I find it absolutely unbelievable that nobody spotted it," he added.
"Council tax bills are the single most important responsibility and it is the most obvious example of when someone should resign.
"They have said Tiverton Town Council had a whacking great 17% rise in their precept when they actually set their budget at zero per cent."
Torridge council confirmed that out of 30,553 bills sent out only 803 were correct, leaving 29,750 wrong.
It said the incorrect amounts differed between different parishes but in most cases bills were £2 to £5 out.
The cost of resending the bills is as yet uncalculated, the authority said.
It add that steps were being taken to re-issue the bills as soon as possible.
Head of paid service Jenny Wallace said there would now be a "full internal investigation".
Council leader Barry Parsons added: "On behalf of Torridge District Council I would like to sincerely apologise for any confusion or concern that this may cause.
Mid Devon council said it had sent out a mailshot of 33,365 incorrect bills, although it said they were only up to £5 higher than they should have been.
The problem related to the share of the overall bill or precept demanded by the town and parish councils.
Conservative cabinet member for finance Neal Davey said the error was made by an officer and was "regrettable".
Mr Davey declined to comment on calls for his resignation but said moves to implement the new council tax support scheme, which is replacing council tax benefit, had caused the error.
"The council has apologised for the mistake which is regrettable and it is taking prompt action to rectify the situation," he added.