Bizarre bill from Spark Energy

NectarCollector

I recently switched my gas/electric supplier from Spark to So Energy. The switch went live on 1st January and I had been waiting for my final Spark bill to be generated.

On checking my account today I found several credit notes had appeared in my transaction history labelled as 'Cancellation of statement x' (cancellation of 5 statements, even though I had previously only had 4 statements, of which I have hard copies.

I used the live chat (didn't want to waste money on a phone call) to essentially be told they have refunded all my previous bills to my account, and then charged me from the date my 1st statement is dated from, to 30th November 2015 in a single bill. Yet none of the amounts credited to my account relate directly to any of my previous bills. In fairness I don't dispute the amount the charges electric/gas amounts to (£567.74 for 26th Feb 15 to 30th November 15). What I do dispute is the amount of credit it says I had BEFORE it credited 5 statements worth of bills back to my account (£742.32) - my account had been £200 in credit at the most.

I half suspect that these are something to do with a previous tenant (The property was supplied by Spark when I moved in - not having any idea about how much electric/gas I would use, I couldn't compare suppliers until I had built up some kind of history to compare)

I was expecting my final bill to be dated 1st October - 1st January, not to be dated for the entire term I was with Spark, I'm certain this should not have happened.