Grounded not paying supplier invoices.

We supp**** Grounded @ Echo with product. We had changed our banking details and it was written clearly on the invoice. They paid two invoices into our previous bank account which was closed. The money was returned to them - but they refuse to pay the outstanding balance into our new bank account. They now have 3 invoices outstanding and I can get no response from Jason as to when payment will be made. The amount adds up to over R5k.