Blaq Rand Communcations - Limitless Marketing

Since November 2017 Blaq Rand Communications there has been going an unauthorised debit order through my bank account. My bank did stop/block the debit order, but after one month, it went through my account again!! Apparently they just change the description a little bit for it to go through. What can I do to stop them? I have been phoning, but the manager is always "busy in a meeting/on the phone". The name Limitless Marketing also pops up when I phone them.