The Driver & Vehicle Licensing Agency (DVLA) has apologised for sending out some incorrect tax disc reminders.
DVLA apologises on its web site for incorrect V11 forms
The forms, called V11s, are sent each month to vehicle owners telling them to renew their road tax licenses.
Some of the tax bands, particularly for cars registered after March 2001, were changed by the chancellor in his budget on 22 March.
But the DVLA says some of three million forms posted since then failed to warn that the rates might have changed.
David Evans, from Hastings in Sussex, contacted the BBC's Working Lunch programme and said: "I received my road tax reminder today, 19 April, from the vehicle licensing people.
"Listed on the form was one year's license fee of £165. I took this to my post office to pay, however they said that the form that they sent is wrong and that it's now gone up to £190.
"Are the vehicle licensing people that incompetent not to be able to produce the correct documents with the correct prices on them?"
The V11 forms are usually printed six to eight weeks before the date by which the licence needs to be renewed.
But they are sent out later, just two weeks before that payment date.
Thus, every year, some V11s are prepared before a budget but sent out afterwards.
Normally they would carry a standard warning that the tax rates might have been changed in the recent budget.
This year, in some cases, that didn't happen though the DVLA says it cannot tell exactly how many failed to do so.
A spokeswoman for the DVLA explained the mistake was due to what she called a "timing error".
In other words, someone forgot to check that all the forms carried the warning.
However she pointed out that the chancellor had reduced the car tax rates for certain types of car and that for some, the new, lower, rates would now be payable.
Another Working Lunch viewer, Michael Goddard from Wakefield in West Yorkshire, was also upset.
His V11 told him to pay £165 but when he logged onto the DVLA website to pay online it told him to pay £190.
"I'm just a bit annoyed as my car is just inside band F, which has gone up from £165 to £190 a year," he said.
People who find they have to pay more than suggested on their V11 will not be able to argue they should pay the lower rate as it is a tax - which is unavoidable.
The AA Trust took a dim view of this mistake by the DVLA.
A spokesman, Paul Watters, said: "We had one of the cheapest car tax systems in Europe but introducing the graduated tax rates in 2001 introduced huge complexity."