Its a pretty common thing now a days, with more power in your hands you can make more people feel sad. This is true mostly about the girls. They, out of their insecurities or the feeling they are not treated well, try to keep the guys on the hook.
What should a person do when someone is not replying to the texts or phone calls? I guess the answer is simple, move on. They have made up their mind not to talk to you and its you how is still clinged to them. Well, you have to move on. what else is there? if you try to stalk them somewhere on social media there are pretty high chances of you getting blocked from there also.
So, The best thing in this situation is to, accept that its not meant to be, and your path is no longer same as theirs.