Frustrated

I have bought a showmax voucher through Vodacom at R99 for 12 months, however when tried to active the voucher it said voucher expired. I went back to the store and was given another voucher to try, that also said expired. We have tried 4 vouchers and all of them has expired. There is no expirery date on the voucher and now Showmax support can not assist in this regard. How do we resolve issues like this is the company themselves cannot give the support required who is liable.