Problems with using earpiece and volume, not turning up or down

Hi there to everyone.
I’m having a strange issue which I haven’t encountered before and I’m not sure when it actually started doing it. When I’m on a call using the earpiece of my iPhone 12 mini not the speaker. For some reason I cannot seem to turn the volume up or down, and I have got into settings And made sure that under sound and haptics is set so the buttons option is switched on for the volume ringer.. I’m just wondering if anyone knows why suddenly the buttons don’t work when using the earpiece of the phone to turn the volume up and down.
Thanks for any help and look forward to your responses.