online shopping

i bought an Edgars voucher via Momentum's rewards programme Multipy, the voucher came in a form of an sms, im trying to buy items online however im unable to use this voucher. i called your customer services, the consultant i spoke to had no idea what im talking about but later said the voucher would not work. i strictly bought this voucher because there was an online special (discount) for valentine's day and do not intend on going to the store to pay for the full price. Please advice how this can be resolved.