Trying to get my sons xbox account to play FC 25 online

So any help would be great as EA support is very underwhelming for a gaming platform.

Ive joined my sons EA account to the xbox account and the game just hangs and wont load , he has been just playing on box for the past year or so and is old enough to go on line... I'm simply out of options based on the help I can see in the account system to know what I'm still not doing right

Ive also tried to link his account to a family account and this never works :( 

Help 

Mat