For those of you who are unfamiliar with the london congestion charge.. The mayor likes a tax of £10 per day for everyone entering his zone.
Unfortunately as well as the official transport for london payment site there are a number of similar sites willing to take your money on behalf of the mayor and charge an extra £6 for the privilege
www.londoncongestion.com is one of those sites that you should avoid ...looks official but is just an agent taking there cut on top of the tax
This is the only official site you should use
(http://www.tfl.gov.uk/)