Help understanding my energy bill

macman

veedub565 said:

I did switch by the way, to one of the cheaper tariffs. I still don't understand it, and the annual quotes aren't a big difference only about £130. The new tariff is £108 a month though not £135 a month so that's cheaper. Works out about £324 cheaper a year. 

So over 10% cheaper. You've saved £130 for 10 minutes work. Or £780 per hour...where else can you earn that?
You haven't saved £324 though. No tariff is 25% cheaper than another. Your DD has been set too low at £108. You need to understand that the DD is not a bill, it's merely a snapshot estimate. Unless your usage falls, you will build debt and your DD will then be hiked to recover it. Look at the annual costs: that is the only figure that matters.