Final bill from old supplier shows credit

I’ve just switched to Bulb and received the final bill from my old gas supplier. This shows a balance of £231 in credit.
Will this credit be applied to my Bulb account or do I need to get the money refunded from the old supplier?

EDIT: I’ve just logged in to the old gas account and see that they show the balance as 0 with a refund for the amount of credit and can see this in my bank account.

This can be closed or deleted if necessary.

This can be closed or deleted if necessary.
I suspect you're not the only person who's had this question so the thread may end up being helpful to others in the future!

For reference for anyone else reading, I believe the only time account balances are transferred between energy companies is when you’re on a prepay meter as you can switch suppliers with up to £500 in debit on your account.
All other times, you will settle with your old supplier, completely independent of your new supplier. If you’re in credit, it’s often an automated transfer but some companies will send you a cheque just to try and keep hold of your money for a little longer.

@foamcow Glad it’s all sorted and the extra information from @mowcius is always appreciated!