Ubereats vouchers expiring prematurely

I received 3 discount vouchers for Ubereats through FNB, and app**** the code in my Ubereats app. These vouchers showed that the expiration date is the 31st December 2019. I used my second last voucher on the 27th December, and wanted to use the last one on the 28th December, just to find it has been deleted from my app.

This is the second time where I received 3 vouchers and after using two, the last one expires ahead of the expiry date.

What's the use of getting vouchers when they keep on expiring before the time?