Voucher code invalid and not providing Miles refund

I bought a Netflix voucher through Discovery Vitality using Discovery Miles. The code was invalid and not being accepted by Netflix. I asked them for a new code. They didn't respond within the time frame specified in their auto email. Later on, Netflix debited my credit card for a new month. I no longer need the Netflix voucher. I then requested a refund of my Miles. I received a phone call over a week later from Farana (spelling?) saying she was sorting it out. That was now a week ago and I've still not received anything back from Discovery.