I have tried changing my proxy settings in a terminal as:

export HTTP_PROXY=http://10.1.3.1:8080

and

export http_proxy=http://10.1.3.1:8080

but when I try to install a new package or update apt-get, apt-get starts displaying messages from which it seems it is trying to connect to a previously set proxy:

sudo apt-get update
0% [Connecting to 10.1.2.2 (10.1.2.2)] [Connecting to 10.1.2.2 (10.1.2.2)

I have tried setting the proxy via bashrc file but that din work either. As far as I remember 10.1.2.2 was set using GNOME GUI but I don't have access to the GUI right now so I am trying to set it from terminal.