[Closed] Energy co gone bust, so what happens now

So yet another energy co has gone bust,and speaking to a freind last week it was a nightmare for her to sort payments out.

So say youre with A company and it goes bust and Ofgem transfer you to another co, do you stay on the same tariff as with company A, or does your bill increase to the new companies tariff probably a lot higher and is it backdated till when they took over.

Also can the new company increase your direct debits overnight to the new tariff or can you opt out and pay quarterly.