Still awaiting a refund for a double payment after 5 months and multiple requests

I am extremely frustrated and disappointed with the above company. They provided a service and were inadvertently paid twice for the service. They were informed telephonically, via email and via whatsapp about the double payment and repeatedly requested to refund. Initially, some response was received and false promises of payment were given. However recent attempts at communication have not been responded to. I have not received the refund to date despite sending my banking details on multiple occasions and sending reminders, I am at a loss at what to do next.