Not able to redeem Evoucher for uv sterilzer on the store

I got the note 20 ultra through upgrade by vodacom. App**** for the UV sterilzer voucher and got it but not able to use it. Phoned and explained, emailed exactly what the issue is including screenshots where it refuses to apply the voucher and asks me to buy it via credit card. I follow up on the emails and get no response whatsoever, got the reference number as well, sort this is out as I do not intend in losing this free uv sterilizer