Based on practice by other suppliers I would expect that excess an in-credit calculation to automatically done and refund supplied once the in-credit amount exceeds estimated usage by an agreed percentage. We are £749 in credit which will take several years to work down at the current rate of usage. There are other posts from as far back as 2017 on this same subject to this is not a new issue for Bulb. I have already sent an email to the help team on my particular case. If you are going to have an ethical, pro-customer image please remember that actions speak much louder than words.
They seem to be having trouble getting all the basics working, which I guess is taking time away from developing the “nice to have” features.
Most customers keep an eye on their bills and adjust their own direct debit level to prevent such high balances from building up.