Closing account - bill failure

Any help would be gratefully received! I have switched from bulb as I never get billed based on actual readings, I have provided my final meter readings but on two occasions my final bill has failed! With over 3 hours of wasted phone calls and nearly £200 in credit with bulb I am being fobbed off! How do I resolve this without me having to go to drastic measures? (I.e county court claim)