Some drivers using the Dartford crossing over the M25 have been double-charged because of a technical glitch, the AA has said.
Toll booth cash payments were scrapped last November after online payments were introduced at the crossing, which runs over the River Thames between Kent and Essex.
But the AA said problems had persisted into 2015.
AA president Edmund King said: “As has been highlighted by the resentment of families who passed on cars to relatives and had to pay Vehicle Excise Duty twice for that month, another new government scheme for drivers has produced unintended consequences – resulting in a backlash from the people it was supposed to serve.”
He went on: “It is particularly galling that any toll remains at Dartford. The tolls and charges were supposed to be lifted in 2003 when the cost of the scheme had been met.
“The new scheme has undoubtedly eased the congestion at busy times but, for some, there is a new concern regarding the behind-the-scenes bureaucracy that accompanies this supposedly high-tech, non-stop tolling.”
A Highways England spokesman said: “As the AA has stated, the vast majority of the 100,000 chargeable crossings at Dartford made each day are processed accurately and smoothly.
“Given the scale of transactions from time to time errors will be made for which we apologise unreservedly. We appreciate the AA recognising that when we are made aware of issues we work with customers to resolve them as quickly as possible. We continue to work hard to ensure that errors are kept to an absolute minimum.”
