Bad service and over billing -

Absolutely disgraceful. They send me a message I am £1250 behind on my electricity bill. This after 11 months, and this after they took £150 for 6 months via a debit order and then £120 per month for 5 months via debit order. So according to them we use about £268 per month on electricity, absolute rubbish. They do not respond to any of my mails, they are impossible to get hold of on the phone, I am currently working through a third party to communicate with them. And what is their answer. We have high electricity usage, absolute rubbish.