Tree2:
There are a few things that can be done. First of all, have you any record at all of the tariff that you selected online when you switched? For the benefit of others going forward always take a screen print because as Tree2 says automated switching and service confirmation emails may not specify the tariff being switched to.
[ This is my experience also. I switched to Scottish Power Dual Fuel NSC and one energy was switched to standing charge and one to NSC, not even a sellable combination. As it happenned I find Scottish Power quite good, if a bit slow, at resolving problems. (Problems emailed generate an auto-response so there is no escape for them if they don't respond) ]
I digress.
Two separate issues here. If you want to switch again go ahead and switch again, I assume to a different supplier, (remember the screen print this time). You say it's a standard tariff so there should be no tie-in. Anyway you'd only be doing what EDF Customer Services suggested.
Regarding your claim, go ahead and make the claim strictly in acordance with the EDF complaints procedure. If you remain dissastisfied after 8 weeks (I believe) you are entitled to ask the Energy Ombudsman to consider your complaint. That will cost you nothing but EDF a hefty case fee well in excess of your reasonable claim so they would be daft not to settle. Which is not the same as saying EDF Customer Service isn't daft.
Regarding the "nothing they could do" statement, I don't believe you were told the truth but that's not your problem.