ATC stops giving directions -ILS ?

hello,

I was flying from LAX to San Francisco, relying on ATC to give me directions and altitude directions all the way as it usually does.

For some reason it stoppped giving me directions and I passed the airport. ATC always gives me directions to line me up with the runway from the start of the flight to finish... but I lost contact with them.

Why does this happen, and How Can I avoid it? Also.. on longer flights, is there a away I can just fly using the autopilots NAV, and contact ATC for directions later, when I am closer to my destination ? And how?

Thanks