'discount voucher'

i got a discount voucher sms 2 weeks ago but I then decided to write the voucher number on paper coz my phone automatically deletes some messages went to Jet Mayfield today to redeem only to be told they have to see the sms on my fone

1.the sms didn't state the store has to see the message 2.I made the purchase of R1200 and was supposed to have R500 off of which I did not get

so please if I can have my R500 back I'll be happy