Shanghai kumai network technology co., ltd. called me and didn't answer.

You can call back. Shanghai kumai network technology co., ltd didn't answer your phone. If you attend an interview with the company or have related business dealings, you need to call back in time, explain why you didn't answer the phone and ask for specific things in detail. But if it has nothing to do with this company, there is no problem if you don't answer, so you can ignore it.