Non existing customer service

These idiots just change a persons contract as it pleases them. I cancelled my contract because they started billing me more than double my monthly premium and now they won't stop running a debit order on my cancelled account(now they are also penalizing me for not paying). I have sent them numerous mails and the auto reply keeps telling me that they will get back to me within 24 hours, but it has almost been a month. They just need to send me an invoice for the outstanding amount(after calculating all the extras which they have ******) but it seems to difficult for them to process, whether it be their system or their brains.