Paid for items yet not allowed to take it home

On 12 June 2024 I made a purchase and paid per credit card and received a confirmation msg from FNB, however the till lost power and after a few reboot attempts the staff got it up but the transaction showed incomplete on their system. I showed the supervisor the msg and the transaction on the FNB App on my phone, but they refused that I take the items I paid for. The staff suggested they ring it up again and I pay again if I want to take the items, which I refused to do. They promised to phone me the next day once they confirmed on their system whether the payment went through. Why must I take the risk despite producing proof that the payment went through? I was phoned on the 13th of June to confirm the payment went through and told I can come into the shop to collect my goods.