What the community manager is afraid to tell you is that you no longer can play online on the Switch if your account is a child account. This is definitely something that EA changed and can definitely change it back on their side, they just refuse to.
Also, unfortunately, Nintendo does not allow to change the birthdate once enter. If by any chance the account is just restricted this can be lifted only if the birthdate enter on the Nintendo switch account makes the child 16 or older. My suggestion is to create a new account for playing online. Yeah this is bad since there is no cross-gaming from the Switch and all the unlocks will need to be done again.
