Did you try adding 00 to the start of the number?
The 1 at the beginning is the international code for the US, so it would be "001 866 543 5435", assuming the number hasn't been changed.
Depending what it's for, you might be able to phone the UK EA offices, although they mightn't be able to help. But on the off-chance they could, it could save you international phone rates.