Been scammed

Dear community could someone please help me out?

Microsoft has taken £80.00 out of our account for something we've never had or even asked for. On 4 seperate occasions they took £19:99 for coins that are supposed to be played on the game fortnite. We haven't even got that game. I put in for a refund and
they've just dismissed us saying we are not entitled to one. That to me is theft/fraud and I need to know what i can do about it. Please help....Mark

:)