I moved my gas & electric last month. As I'd been with my previous supplier for about ten years I (wrongly) assumed that they'd make a decent estimate of my final bill and charge me accordingly. When they asked my for £93 i thought it was a bit steep, but I've not made any increases to my payments for a while so i thought it must be right. Then when I was asked for meter reading from my new supplier I realised just how far out my old supplier was, so I challenged them.

Turns out they now owe me £134.

Result.