If you just purchased it, take it back in to the store you purchased it for an exchange or refund.
Otherwise, if you call in for tech support, they will more then likely suggest a series of steps to troubleshoot and possibly diagnose the issue, one of the biggest being a factory reset on the phone. This is my best suggestion without knowing any more.
Simply back up all your data, photos/videos/texts and calls via Google Drive, Google Photos, SMS Backup (app on the Google Play Store), and restore it once the process is done. But of course, first check that the issue is fixed when you do a factory reset.
Good luck!