03456 numbers are not free on EE (nor are they free on any other phone company) however you can call them using your free minutes if you have any inclusive minutes in your Pay Monthly contract or Pay & Go top-up bundle.
If you have no spare free minutes, the call will be charged at “standard rate” – equal to calling any 01, 02 or 03 number. This is the same pricing policy that all telecoms companies in the UK are bound by, due to Ofcom’s reforms of the industry in 2015. Please check with EE to find out the exact cost of a standard call under your current tariff.