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Since then, Scottish Power has been appointed as the supplier to take on its 74,000 customers.
As they have now taken over control of the accounts, you will need to apply to them to get your credit refunded, according to Ofgem, the energy watchdog.
Scottish Power will honour customers credit balances for both current and past customers of Yorkshire Energy who are owed money.
Ofgem advises that customers wait for the supplier to contact them with relevant instructions.
However, the review process may take a several weeks as Scottish Power needs to receive and review records from Yorkshire.
When calculating your credit balance, they will deduct any unbilled charges for your supply by Yorkshire.