refusing to refund

They are refusing to do a refund to my account after I was incorrectly debited a very huge amount, I keep getting told the refunds can take up to 5-6 weeks but no one can explain to me why it is taking so long . Zoom fibre who handles the installations had confirmed that no work was carried out , its been over 2 weeks and no one has called me except when I text them on whatsapp