First flat, need advice.

Stiggy

If you don't need the prepayment meter you should get it swapped. Although the tariffs have improved I still suspect you end up paying more on prepayment.

Storage heaters are a pain, and it can really bump up your bills if you don't use them correctly. I am on economy 7 and try to use as much energy overnight as I can; washing machine, dishwasher etc.