If you do not think you are in credit by £200 then look at the bill again, maybe it says you have paid in (credited) £200 but have used electricity to that amount and the final figure is close to zero? Credit at the bottom line of a statement means they owe you that amount, but credit as part of the calculation means what you have paid in to pay for the power. Hope this helps.
Hi if you really have that much credit then you should report it to 0800 027 0072
I think though that what you are seeing is the total amount paid in (credited) on your account and the bottom line probably shows you have used all that fuel and do not have a high balance remaining. Pre payment meters do not build up huge credit balances.
@tgl49 I think what you are reading as credit is the total of all the payments you have made on your Payg meter.
Your available money for power is totally different.