Dollar General review: Gift card I purchased was denied at the store I tried to use it at

I purchased $450 worth of gift cards on 12-15-2023. When paying, 1 of the cards was rejected, so they gave me a refund and I purchased another card to the same store for the same amount. I gave this card to my grandson & his mother used it for a purchase at the store. At that time, the card said it was denied, so she had to pay cash for the purchase. She gave me back the card and I took it to the store where I purchased it. The cashier said it would take a while to check into it, so she told me to come back later. I came back in an hour and she said the card had already been used and your fraud dept. would check into it & call me back. That was last week, and I haven't heard anything. I called my bank & they said to keep contacting you & if this is some type of scam, you would refund my money. I am a senior citizen & I feel we are taken advantage of. I am not going to give up on this, I paid $50 for this card & that is a lot of money for someone on social security. I would really appreciate you checking into this matter. Thank you