Please reset network setting of both Sim one by one and than reset all settings of your's device in general management settings also Flight ✈️ mode on n off one time, restart your's device without any Sim in slots also interchange Sim in slots, turn off power saving mode then try to it's again. If you like please accept as a solution it's help to others users also,click on 3dots in my reply section and click on accept solution. Thanks.
U can try the following, 1) boot ur phone in safe mode & see if the issue persists 2) during the call press "Vol up" button to see if the vol is at max or to check if the button gets pressed automatically due to mobile case(cover) 3) goto calls & clear cache & data(don't forget to take the backup of call log). 4) see if volume monitor settings are as per ur need. 5) try with different sim of same as well as another network & see if the problem is with network in general or with specific service provider. 6) last & final visit service center or try soft reset of ur phone 7) Alternatively u can hard reset also but again don't forget to take the backup of ur phone data.
In case the issue still occurs, kindly report the problems with a log file. To share a log file, click on the Samsung Members Application (Open Samsung Members Application > Support> Tap on error report > Type your query > Send).
