Unable to redeem voucher

I recieved a voucher from Ackermans i think in November. Then in Decemeber i recieved two sms reminding me to redeem it before 31 Dec. However i have now tried on two occasions to redeem the said voucher with no luck. <br> First time i was told i cannot redeem it on a ietm that was on sale. The second time i was then told i could not redeem it at a Dunns store which is linked to the ackermans group.