Both are fine. I call it football - but that’s because I’m from the UK and it’s always been football to me. Logic: You use your FOOT to kick a BALL.
The origin of soccer as a word comes from association football, which was established in England in 1863 when the Football Association set standardized rules for the game. People often accuse American’s of starting the trend of calling it soccer. In reality, the terms for the sport or interchangeable and both are correct.
Throughout my life, I have only known football by the name ‘football’ since birth. I use the term ‘soccer’ during messages when discussing with friends in the United States to prevent misunderstandings.
The FA cup is the OLDEST competitive tournament out there if I am not mistaken.
My love for the FA cup is becuase it is anyones game. You can have teams like Dundee United playing a powerhouse like Manchester United.
I am the same way - it really seems that soccer is primarily used in North America, where football is more commonly used in South America and Europe.
Or, the rest of the world.
Errm, I beg to differ. Manchester United is not a powerhouse, at least not anymore. There’s nothing powerful about a team languishing in the bottom half of the league table. 
I think they call it Soccer only in the US and Canada… Even in the countries where American language and culture is dominant, the still call it Football when they want to talk about Soccer. I call it football