Family Dollar complaint: $5.00 Discount coupon

On November 15,2020, I bought over $25.00 worth of merchandise from the store and hoped that I would receive my $5.00 discount as I clipped my coupon and thought the deduction would happen at the register; however, no discount was applied. So I paid the full amount but quickly returned prior to leaving to have the Manager Nicole return the items I purchased and scan the discount bar code off my phone to apply the discount. Nicole had trouble with the bar code scan so I asked her if there was something that she could do and she insisted she could not! This is not a isolated incident with the same Store Manager NIcole as I previously tried to redeem my $5.00 on about a month ago and had the same problem! Although Nicole admits that I did everything correctly; she claim that Family Dollar has her powerless to make any exceptions of credit toward customer accounts. Why is she there if she can not satisfy your customer?