What should I do if I send text messages to my former classmates and ignore me?

The reason why she didn't reply to your messages may be that she didn't feel anything for you, or she forgot to reply too many messages.

If it is the first case, it may be that things are different and you can only let nature take its course;

In the second case, I suggest you find a suitable time to ask her out to meet and talk, and maybe you can renew your friendship.