REFUND DENIED

I came home the other day to my son very upset and guilty, saying he'd bought things on Fifa 21. When I checked he had bought nearly £80 of in game items, basically double the price of the game itself. I attempted to get a refund for the purchases but was denied without any contact from Microsoft or an explanation. Does any one know how to attempt to dispute when a refund gets denied?

Sincerely,

A long term and very angry customer

:)