Gift voucher it's not safe

I bought a gift voucher of 5000 on the 11 march this year and on the 14th I got ****** my handbag and then on the 18 I went to the store to block the card and to check if it was used maybe ,well I was told they can't check the balance nor block it even worse the can't replace it ,I was shocked to learn that as I did found the option in their website about checking for a Balance but they claim they can't please help me resolve this matter