The DD advice is likely automatic ... it will be refunded or c/f to your new energy supplier ... if you are expecting a refund Symbio or whoever is dealing with Symbio a/c might not be able to process the refund if you have cancelled the DD which has your bank details.
I have a credit balance with my old supplier, OVO ... and a credit balance with my new (but failed / busted) supplier AVRO ... I know the OVO balance plus this week's DD to them will be refunded back to my bank a/c ... and the AVRO credit balance will be transferred to the allocated new supplier Octopus ... when i'm officially advised of the Octopus a/c being set up ... always takes a few weeks to sort out ... no need to panic