What could be wrong with him?

So I have been dating this guy for 3 months now and things have been great! However, last Thursday night he just stop texting me out of the blue and I text him once Friday and no answer. Then I called him saturday and a operator came on saying "the number you have dialed is not a working number please check the number and try again." Could it be that he changed is number or he hasn't paid his phone bill??? What do you think it could be? Please Help!!