Hello, yes I have used a named instance.

I have found a solution to the issue I was facing. Have done the following (other than firewall settings, which were done earlier):

1....

Hello everyone, thanks for your suggestions and support. I have got the following results from my trial and error:

1. We are able to connect to SQL Server 2012 through VPN...

Now, today, even if I disable the local firewall, I am not able to connect to SQL server

Fixed port no. 1433