McDonald's moment of disappointment

This is regarding the #MomentsOfLoving which was on twitter ,i shared a picture of me and my son and his father .and I was told to DM my info because there was a little surprise for me .so i sent them my details . i got a call back from them and they asked me for my email address and within an hour i received an email with the voucher code that i could redeem at any store . I was excited . but the excitement was short lived when i went to the McDonald's at Jean crossing and they tried a few methods to get the voucher to work , each time it said declined. I then tried again at the McDonald's in Pretorius street.I thought okay let me DM them and inform them about the issue with the voucher . when they eventually answered they asked which branch i was had this issue with , I told them and that was on the 23 of October . I haven't heard anything from them since , I just hate that they completely ignored me . why give people vouchers that don't work and not try to fix the issue or even the decency to just reply