I have been using my Samsung S8 for just under 2 years. I have been on id mobile for about the same length of time.
In the W6 postcode, I have always had perfectly fine call quality. However, in the last few weeks, I have repeatedly been receiving phone call problems. Either the caller cannot hear me; or I cannot hear the caller.
The problem disappears when I use other apps (e.g. Facebook Messenger or WhatsApp) for video calls, so I know that it’s not a problem with either my microphone or speaker.
Maybe the id mobile network is overloaded and I should change to another network?