Cannot initiate the connection to archive.ubuntu.com

I am unable to update or install any packages through sudo apt-get Following works: ping google.com wget google.com However, apt-get commands fail with an error like:

E: Failed to fetch http://archive.ubuntu.com/ubuntu/pool/universe/m/mesa-demos/mesa-utils_8.4.0-1build1_amd64.deb 
Cannot initiate the connection to archive.ubuntu.com:80 (2620:2d:4002:1::103). - connect (101: Network is unreachable)
Cannot initiate the connection to archive.ubuntu.com:80 (2620:2d:4000:1::19). - connect (101: Network is unreachable)
Cannot initiate the connection to archive.ubuntu.com:80 (2620:2d:4002:1::102). - connect (101: Network is unreachable)
Cannot initiate the connection to archive.ubuntu.com:80 (2620:2d:4002:1::101). - connect (101: Network is unreachable)
Cannot initiate the connection to archive.ubuntu.com:80 (2620:2d:4000:1::16). - connect (101: Network is unreachable)
Could not connect to archive.ubuntu.com:80 (91.189.91.81), connection timed out
Could not connect to archive.ubuntu.com:80 (91.189.91.82), connection timed out
Could not connect to archive.ubuntu.com:80 (185.125.190.39), connection timed out
Could not connect to archive.ubuntu.com:80 (185.125.190.36), connection timed out
Could not connect to archive.ubuntu.com:80 (91.189.91.83), connection timed out

However, I have already tried common solutions like:

sudo apt-get -o Acquire::ForceIPv4=true update

But this also doesn't work. **Note: I am behind a proxy**, with following environment variables sourced:

export HTTPS_PROXY="http://proxy.xxx.ac.in:3128 "
export HTTP_PROXY="http://proxy.xxx.ac.in:3128 "
export https_proxy="http://proxy.xxx.ac.in:3128 "
export http_proxy="http://proxy.xxx.ac.in:3128 "

Please suggest how to resolve this issue. Thank you.