I had a contract with So Energy for many years and built up a credit balance. I asked them to refund the credit and they refused, repeatedly. Eventually I closed my account, making sure my account balance was zero and reported them to the regulator who agreed they should have refunded the credit balance and fined them £75. Which they paid. And to my surprise, a year later I found they have now put a notice on my credit file that I owe them money. Of course I've filed an objection at the credit agency. I recommend to stay well clear of this dishonest company who went downhill fast after they were acquired.