It sounds like you didn't have a signal for a while. If you don't have a signal then callers will be sent to voicemail.

I guess its an delay connection of the signals due of having heavy weathers ..

I recently switched from sprint to cricket and the vendor did a full flash. No problems whatsoever. But we misplaced the phone so we got a new one. So that 30 dollar phone gave out in a month but luckily
by that time, I found the old sprint phone- galaxy s2 epic touch- and went over again to the same vendor to activate it. Soon enough within hours we didnt realize we had 6 voice mails, saying we've been trying to call you, get a hold of you but it just send us straight to voice mail. Any bit of advice can help. Thank you.