Green Star Energy

It is absolutely horrible. I signed up to Greenstar half a year ago with a payment via direct debit. For a couple of months, I did not notice any payments for my bills. A couple of months later I received a letter stating that my case was passed to Debt collection agency. When trying to contact them to sort out the issue, I was told that I need to contact Debt collection agency and that they are not going to deal with this matter. On numeral occasions, I have tried to contact them with no response. I also had problems with my online account as they never set it up for me, and when trying to get a login, a Greenstar advisor said they would solve the issue, but they did not. I have switched to another provider, but I have no idea what to do now as I still want to pay the debt but have no idea how.