Putting the number into Google returns results that suggest that this number is for Seeboard and
this E.ON Energy contact page says it's for "MPAS - EDF Energy Area" and this comes under the heading "Formally Seeboard".
Seeboard was the South Eastern Electricity Board and this is now run by EDF Energy. MPAS stands for Meter Point Administration Service.
It stands to reason that your local network operator (what used to be the electricity board) would know who your supplier is. It would appear that you need to speak to its MPAS.
Searching our database for
seeboard
returns one result:
Seeboard Energy (EDF Energy) 0191 522 1103 0800 0969696 Customer services
You may have to explain what it is about; perhaps ask for MPAS.
Failing that, search for
edf energy
and take your pick.
Let us know how you get on and what, if any number, is a successful alternative so I can list it for others to use.