Why is he doing this to me?

We broke up for close to two months but we still exchange text to each other more of sending regards and etc. I texted him since the afternoon and haven't gotten a reply past midnight. He was online but he just ignore my text. I couldn't take it anymore so I called and asked why he ignored my text but he could reply to others when he's online? He said he didn't check his phone. Are you serious?! Why is he doing this to me? I rather he be open and honest if he wants to cut things clean.