I had been a customer for 2 yrs. I was unable to enter my meter reading on their system as it often would allow me access and after explaining that I had a physical disability, they agreed to treat me as priority and would receive a representative to visit my home and do the meter reading. I was in credit in early 2019, but then when I decided to go to another provider, as advised by Martin Lewis to compare prices, I was hit with a bill in November 2019 for the amount of £933.67; this amount was the final bill in August 2019. I tried to gain a reason for the amount without any reply, then in April 2020, I received written and email correspondence from a debt collector. I commenced a dialogue with them, forwarding the 2 yrs bills I received from one of their colleagues during my dialogue with them in November 2019. I did not hear anything further, but then today, 17th December 2020, I received a letter from a law firm whom Green Star Energy have instructed to recover £1,354.99; Green Star Energy, who are now under Shell Energy Retail Limited; they have added £421.32 after my contract had ended. Just how Green Star Energy/Shell Energy Retail Limited can instruct a law firm, so can I. The one good thing that goes in my favour was that I asked for copy's of all my bills from the time I was in contract with them and can show what the final bill was. So for anyone in dispute with a energy company, request copies of your bills and keep them as evidence in the event a discrepancy may arise. I will keep you updated but intend to bring this matter to the attention of Martin Lewis team.