The online servers were due to be closed down on May 10, there is a thread at the top which says that.
However, I think what confused people is that online servers were NOT closed down then and indeed I and others were able to play until a few days ago.
I think they may have now been closed down finally 4 weeks after the scheduled date! in which case it would be so much better if the error message could say something like " Fifa 15 NS has now been taken offline". Unfortunately, transparency is not a strength of EA. Indeed the message suggests the problem is temporary! Why can't EA get something as simple as that right. Not everyone will have read the message or indeed will even come to this webpage.
@EA_Andy @EA_Guy