They should not be available, if your proximity sensor is working fine.
That sensor, when you use your iphone close to your ear, should prevent that behavior.
Three things to try:
A forced restart of your SE, using these instructions:--> Force restart iPhone – Apple Support
Check if anything (screen protector or cover) is interfering with that sensor (it is located close to the earpiece at the top)
If the issue still persists, have your SE checked at an Apple Store or AASP:--> Apple – Location Selector
Regards
Giulio