what to do with first utility.

ollski

I am in the proccess of leaving f.u to go back to bg and just had my last bill. They have over estimated my gas bill for the last 14 months as my smart gas meter has never worked. I now work out that they have over estimated by about 500m3. I have phoned them but obviously as this is f.u it will never be acted on or resolved so what would you do, cancel the DD for the final bill and wait for an accurate one running the risk of damage to your credit file or overpay and hope to recoup it suspecting that will never happen?