I discovered on Christmas Day that the vouchers I sent to two young relatives have been useless... but the company (one huge river-like online retailer) is not replying to my calls.
I get initial customer support then referred to another team who do not call back.
The first voucher was intercepted by a stranger (customer support told me this) and had been used. I guess it is easy to identify a boxed voucher- but it seems that senders have no more protection than if they sent cash. I had no idea.
The second was used to open a new account with the retailer and was then suddenly closed by the retailer. The recipient lost access to the voucher loaded on there.
I am still hoping to get this last one back ... but apparently have no refund rights.