@Huss It depends on your account PAYG gets a voucher or credit if it is a smart meter. Normal meters get a credit to the account. In some cases a cheque might be sent but that is unusual.
@burnham You say HMG (Government?) say you get Warm Home Discount automatically. Yes, the core recipients get it paid directly from DWP as part of your benefits regardless of your fuel supplier.
The second level of WHD is operated by the fuel companies and involves an application which you have to make each your giving details of the benefits which you receive. The fuel companies then pay out the benefit as a credit to the fuel bill. It is at the fuel companies discretion to accept or reject applications. If they accept an application they send you a reference number to support your claim. When they pay out the money is reimbursed by DWP, but the idea that power companies sit on the money is not correct. Administration has been put into chaos by the Covid situation, but if you have a reference number there will eventually be a credit added to your account. You can remind SP by quoting your reference number in an email to