The association's magazine Which? also claimed that compensation payments for travellers who have been inconvenienced by delays and cancellations are both confusing and inconsistent.
In a survey of four rail companies South West Trains - which had to cancel dozens of trains every day earlier this year - was rated the poorest in providing passenger information.
When Which? sought information from the National Rail Enquiry Service (NRES), it got incorrect details in 41 out of 70 cases.
Researchers said that the service gave the right price just four out of 21 times when they asked about the cost of travelling from Basingstoke in Hampshire to Carlisle in Cumbria and returning via London.
Some NRES staff told passengers to buy two single tickets for nearly pounds 120 - pounds 60 more than necessary, Which? claimed. It found the service gave wrong information about engineering works that might affect travel times six out of fourteen times.
In a survey of passengers using Connex South Central, South West Trains, ScotRail and West Anglia Great Northern, Which? found that the latter had the highest commuter rating for providing information and SWT the lowest.
"Many people would like to switch to public transport but are unlikely to travel by rail if they can't rely on getting the correct information," said the magazine's senior editor, Andrew McIlwraith.
The Which? findings follow warnings last month from the rail regulator, John Swift, that train companies faced big fines if the performance of the NRES did not improve immediately.