Video report from ITV News Meridian's Tony Green
More than a million pounds is locked in Dartford Crossing payment accounts that have been automatically closed after not being used for 15 months or more.
A Freedom of Information request has revealed that nearly 78,000 motorists are affected.
Money Saving Expert, which lodged the request, says those affected will be able to reclaim the cash.
Steve Nowottny from Money Saving Expert on getting your money back
"You'll need to contact Highways England or log into your account to see if your account has been closed. And then if it has been, you'll need to call up the Dart Charge customer service people and ask for your money back" says Steve Nowottny from Money Saving Expert.
Locked in inactive accounts
What is a Dart Charge account?
Drivers who use the Dartford Crossing would normally pay £2.50 per car every time the crossing is used. However, drivers who set up a Dart Charge account would be charged £2 per crossing.
The money is added to the account prior to using the crossing which also decreases the chances of forgetting to pay the charge and then receiving a fine.
If the registered vehicle doesn't make a crossing for a year the driver will get an email saying they must use the crossing in the next 90 days or their account will be closed, even if there is money still in there.
Drivers won't be refunded automatically and if they later use the Dartford Crossing their accounts would not be reactivated. This means they would be fined if they didn't use an alternative method of payment.