Hi,
It sounds as though the electricity is having a registration problem.
When you transfer your energy supplies all the metering information is sent electronically from your old supplier to the new supplier, however to lengthen the process this information is sent to other third party groups in the energy network. This is so all the other parties are aware of the change and can amend their records and so the details can be validated.
Your case sounds like the metering information has stuck with the third parties, the gaining supplier in this case have to await the information to arrive. There is a process in place for this to be chased and resolved, however this sounds like it has been ongoing for much longer than it should.
Call E.ON on their complaints line number 0845 300 6301 and request a full investigation.
Brian
Employee of E.ON