Faulty new app

Last week I logged a complaint regarding my Starbucks voucher that disappeared when FNB upgraded their app. FNB just got back to me saying that they can't send me my voucher because it has expired. Offcourse its expired now because it's been more than a week that my voucher disappeared when their updated their app. I want a new voucher because it was still valid when it was on my old app and disappeared with your new app. FNB does not want to take any responsibility for their faulty new app!