Vitality refusing to reimburse cash back and not responding

Its been 18 days since my initial enquiry and no informative response. Vitality never reimbursed the cash back for products that I bought at Sportsmans warehouse with the Vitality logo on. Now they're ignoring the issue. Seems like they are doing all they can not to have to pay. Very sad really. Not the company customer service that you would expect from a Discovery linked product.