MTN Groceries Voucher Winner

Good Day Hellopeter I have a negative review about MTN South Africa via Facebook, I entered the MTN Groceries for a Year competition on Facebook,a few people I know have entered and won too,the problem is I received my first 4 Vouchers, each voucher is worth R500 which we receive every month,the voucher I received in April and May, according to the ShopRite cashier's it declined and does not work,each voucher has an expiration date for each voucher,both April and Mays vouchers declined at ShopRite Mini Lenasia south,I left empty handed and embarrassed,left the groceries behind both months it did not work,I contacted MTN, according to MTN it shows on their side that it was redeemed at the very store I went to purchase,ok so I left it did not argue with MTN because probably the cashier's redeemed it, so June comes I get my next voucher,it worked,July and August I did not receive the vouchers, everyone else who entered besides one lady has the same problem as me, everyone received valid vouchers,so I've been messaging them from July , they promised to investigate as to why I didn't receive my SMS with Wi Codes for July and August,it's been too months begging MTN to do the right thing with daily promises that they will look into the matter, escalating 48 hours for every second day till date ,they apologies all the time nothing is done,I'm really dissatisfied with the service of MTN and false promises daily,I've been a MTN customer for over 15 years and I'm not happy,they need to do the right thing and be Fair and give me my vouchers I fairly won just like every other person. Please assist,I'm fed up with this issue,it's not fair on me.