EXPIRED VOUCHER

I have a Spur Family card and recently received an SMS from them to advise that a voucher was due to expire: <br> <br> Dear Spur Family Card Member: Vouchers on your card ending ***1 will expire in September. Visit your local Spur now to redeem. Reply STOP to opt out.<br> <br> I decided to make use of this on 18/09/15 and when it came to paying the bill, I was told that there is no voucher available. As you will see there is NO expiry date on the SMS. What I fail to understand is that I have used other vouchers prior to this one - why was this one not used first?