@urzz06 A couple of things to bear in mind... If you switch, you'll almost certainly have to pay that balance to SP in one go, however your complaint goes and whatever any subsequent OS finding may be. But even if The OS finds in your favour, there's no telling what (any) compensation might be... some people have only received a token payment awarded, which says more about (an energy provider) being wrong than in any way compensating the customer or punishing said provider. On the other hand, the cynic in me feels SP would not be hilighting your freedom to switch if they were 110% confident of their position.
If you don't switch provider but switch to a more appropriate tariff within SP, they might be more ameanable to a reduction in that charge, subsequent to your coming to an agreement in the complaint arena. Might be worth thinking about... You'd also get 2 yrs to pay back what was (possibly) agreed, however large or small.
I do not know your usage or lifestyle, but for over 5 months of energy use (through winter) £700 isn't actually that bad a figure for my household. Might be worth looking at your historic usage with an objective eye to see just how over-and-above it really is for yours.
How certain are you that your ExEn account was in arrears? All the people I've seen on here think they're owed. If you are owed too, switching will in no way jeopardize your claim, and when it's finally sorted, you'll get it back, not SP.
Some tough choices there. I don't envy you.
Of the people who have received money from extra energy, how was it received. I have been holding off from paying my bill to scottish power and from switching tarrif in case this will cause a problem but so many months on now i need a solution. Any advice very much welcome please.