Used Voucher

Hi,on the 19th of March i went to one of your store @ Mall@Carnival,my lay bye had expired the store manager told me they now refund us in vouchers i was given a voucher which was printed and also sent virtually,today went to the same store to redeem the voucher but i never redeemed it,so would like to know where it was redeemed because i feel like i was ****med by the store