Can some one explain this bill to me?

[ABitCrapReally]

I moved out of a rented place on the 1st July this year. Had independent inventory done with Gas and Electricity readings. I sent these off to the supplier, received a final bill for £84.97 which I paid.
My account was in credit so they refunded me the excess. I cancelled my Direct Debit.

2 days ago I get a credit collection agency tell me I owe energy supplier £36.84
When I phoned energy supplier they said they were given meter readings on the 15th by Landlord before new tenants moved in.
I have sent them proof I moved out on the 1st and sent the inventory report with meter readings.
They sent me this bill, but I don't understand it? Can anyone explain where they are getting the £36 from?

They refunded you too much. They owed you 667.48 plus the 126 that was paid as well, so 793.48. You owe them 84.97. Which means they owed you 708.51 but they credited you with 742.25 instead. So you or them the difference - 33.74.

That explains it

But what about the VAT? Charges before VAT 81.05, VAT at 5% 3.92 ??

Where does 3.92 come from? 5% of 81.05 is 4.05