Dial *888# and u will go to Mobitel Self Care.
Then Go to "Activations & Deactivations" using NUMBER 2
Then u will find "Miss call alerts" under NUMBER 4
You can enter your name(only 12 characters) and activate your miss call alerts.
If this is not working,Go to your Phone settings > Call Settings > Call Divert > and divert your calls(when busy,when not reachable etc) to +94710111000.