One UI 8.5 brings a new feature of direct Voice mail on every Galaxy devices, from low to midrange to flagships.To unlock the feature:Open 'Phone' app> 3 dots> setting > 'direct Voice mail' > turn it on.Or search for 'call setting' then you can find...
Check with other sim cards if it continues then visit service center. Also you can diagnosis via samsung members app whether problem with all network or only with airtel.
