In settings I have selected "Reject by" as "Send SMS" but still the application doesn't send any SMS to caller on rejection. I can see this in Logs also as the rejected call is shown as it is rejected by busy tone rather than SMS. Why?
This happens when you ran out of credit in your SIM. This is because every call is first rejected by busy tone and after that SMS is sent to the caller, so if you have no credit then no SMS and hence no log for Reject by SMS.