Discovery Rewards Cotton On Vouchers

I purchased a Cotton On voucher using my Discovery miles. I then tried to use the voucher at a Cotton On store and I was informed that the voucher has already been redeemed. I contacted Discovery and the company’s agent told me they are aware of the issues with the Cotton On vouchers. I don’t understand why no communication has been sent to clients. If I had known about the issue with the Cotton On vouchers I would have never used my miles to acquire one!