Poor customer service from EDF Energy

EDF Energy provides electricity and gas supply to homes in the UK. I have no particular issue with the actual supply. The problem is their customer service and being impossible to communicate with.

I vacated a property on 30 October 2018. New tenant took occupancy. But I am still getting the bills/accounts. I took it up with the estate agent who advised that the new tenant has contacted EDF Energy.

In addition I sent the final meter readings to EDF, along with the new tenant's lease agreement ,and asked them to send me a correct final bill. And still I get another bill for GBP 278 up to the present time (Feb 2019) Every time I contact EDF I get a different person and have to go through the whole process again. Still nothing happens. Emails have been going back and forth for nearly a month. Each time I send them all the details mentioned above, and we are still no nearer getting this sorted out. Poor customer service.