Joined Together Energy when I rented a house for a year. Despite countless hours on the phone with them trying to set up an account I never received ANY email, letter or bill from them. The experience of their customer service was an endless cycle of calling them, explaining my entire situation from scratch, including giving initial readings, listening to their half arsed apologies and assurances that someone would look into it and call me back - then I would hear absolutely nothing. Repeat.
Utterly frustrating.
6 months after moving out and closing the account I finally received the final bill - my first ever bill.
Under ofgem backbilling rules, energy companies can't charge for usage more than 1 year ago so I'm not paying it until they correct it.