There are worse power companies to deal with than ScottishPower, I think you will get it sorted. There are no penalties for running out of credit (other than having no eleccy).
It is difficult to see how this has come about, there is no seasonal weighting with single rate eleccy (unlike gas), unless it was economy 7/white rate or similar which may well be seasonally weighted for the same reason as gas (to level your bill over the year and avoid bankruptcy in winter).
In a time of universal deceit - telling the truth is a revolutionary act. George Orwell
When the debate is lost, slander becomes the tool of the loser. Socrates