how to disable amex notifications on a sons phone ??

my sons iphone 12 died .. went to apple store they did a swap and during the setup i added my amex card to pay the diff and 'look cool' with the apple pay touch pad they had at the store.. i then removed the card from my sons apple pay .. To this date .. my son sees ALL transactions on the card .. Amex only has my number for notifications. they said its a defect with iPhones and i should contact Apple .. hence this post . please advise on fix to stop Amex notifications showing on diff device after it is removed from their wallet . thanks