EXCEPTIONALLY POOR KULULA SERVICE

Booked specific seats and paid for them. On arrival these seats had been given to another two passengers, the excuse was that the plane had changed but it had exactly the same seating arrangements. Now trying to obtain a credit for their error is a nightmare. After 10 days they are still not able to confirm that the credit has been processed and I was told the refund takes between 6 to 8 weeks. What kind of service is this.