Diagnosis
Since you've tried fresh batteries, the issue is either the remote's IR blaster has failed, or the projector's IR receiver sensor is blocked or malfunctioning.
How to Fix It
First, test if it's the remote. 1) Use your smartphone's camera (the selfie camera usually works best). 2) Point the end of the remote at the phone's lens and press any button. 3) Look at your phone screen. You should see a faint purple or white light flashing from the remote's LED if it's transmitting. No light means a dead remote.
If That Didn't Work
If the remote lights up on your phone test, then the projector isn't 'hearing' it. Check that nothing is physically blocking the small IR sensor on the projector's front panel. Also, ensure you're not trying to use the remote at a extreme angle; it needs a fairly direct line of sight. Bright sunlight or other strong IR light sources (like some LED bulbs) can also interfere.
Heads Up
You can download the 'RemoteNow' app for Hisense on your phone as a temporary workaround—it controls the projector over Wi-Fi. If the physical remote is dead, you'll need to order a replacement (model XRC015P is common) directly from Hisense or an authorized parts dealer.