Shell Energy - Bill Issues since being moved from Green Star energy

ianfitzgibbon

Hi everyone 
Hope you are all well
Has anyone had issues with Shell Energy since  the moved you from Green star...  basically i was switched on 1st July this year and then they said I owed them £325.  Basically affer many calls and emails to them I am now speaking to someone in the customer service / resolutions team who said that the issue was I had an account incorrectly opened by Shell in March whilst I was still with Green star.
I have asked if the erronious amount could be wiped out in readiness for my first bill - Oct/Nov this year and they have said they can't as its a "new process" and is with the backoffice team to resolve and they currently do have a resolution .
I want to leave Shell but I am stuck between a rock and a hard place - can anyone give me some ideas how to sort this please 
Kind regards 
Ian Fitzgibbon