Lumia 1020 :: Call Dropping On 2G Network

I have strange issue with my phone.
Calls on my phone drop almost certainly when I'm on 2G network. When on 3G this rarely ( or almost never) happens.

Same sim card works very well in other phones. This is issue is just on 2G network. I do not get 3G network every where so i cannot ignore this issue.

Nokia care unit says this phone might have hardware issue and quoting about same amount of repairs of cost of new phone. They claim this needs to be sent to factory for repairs.( this phone is out of warranty in region where I am using it).