iPhone 8 Microphone Muffled during Phone call

Hi There,

i have an issue recently ( i think after updating to ios 13.4 )...

i have iphone 8 & using iOs 13.4.1 ( latest ) & when i'm using "phone" ( cellular call ) my voice is muffled to other people & they cant hear me & ask me to speak louder...when i put the phone to speaker , they hear me clearly...

my iPhone microphones are working fine in other apps ( voice memo - video recording - whatsapp & all other apps ) and i only experience this problem in cellular phone

my phone has no case or protector to block microphone + no dust or ... on microphone & i tried these :

reboot - hard reset - restore ( using iTunes ) - turned of noise cancellation - changing cellular to 2G/3G/LTE

what should i do ?!