Samsung note 2 Long distance call receive issue

Got Note 2 on 26th Dec 2012.

In last around 20 days of use I found out when my friends and family members are calling me from India sometimes I don't receive the call details on my Note 2. I came to know about it after 2 weeks of use when they started complaining saying I didn't return their call. Fact is I didn't receive it.

I did a check on this couple of days back while being online with my few friends and asked them to call and 4 out of 10 times I didn't see the call in my note 2. I tested it from cellophane as well as landline. And the nature of this issue is very random and no pattern. One day you will get the calls and other day you will get 50% of it.

I called Att helpdesk and tech support twice but no help. It has been only 20 days of my 2 year contract and I have this big time issue.

Did anyone face this issue? is this my phone or At&t network or something else. How to resolve?