Can't update because the word prox* is blocked
The packages get blocked because your government apparently uses a URL filter. You can circumvent this by using FTP instead of HTTP to upgrade. To do this edit the file /etc/apt/sources.list and replace all occurrences of http with ftp.
You can also do it with these commands in a terminal:
sudo cp /etc/apt/sources.list{,.old}
sudo sed -i 's/http/ftp/g' /etc/apt/sources.list
Now try to update your package list and install the updates
sudo apt-get update && sudo apt-get upgrade
You will need to repeat the process for additional software sources (i.e. PPAs) that live in the directory /etc/apt/sources.list.d/. (credit goes to reddit user noname-_-)
Other than getting some unofficial packages you can not really trust if you do not know the source you can download distribution CDs and DVDs as an .iso file directly from Ubuntu:
- Ubuntu CD Images
By browsing there to the version you are using you will also find most recent daily updates from where you may be able to install updated packges (they may not be stable though). This is e.g. a link to the 12.04.2 daily build DVD.
Here also is a list of download mirrors, some of which may be better accessible for your:
- List of Ubuntu Download Mirrors
Note that you still will not be able to have immediate security updates from packages with a banned word in their names.
Use a VPN.
Free VPN -Google
With a VPN you connect to another computer, from there you connect to the mirrors. The connection is encrypted so there's only the URL of the VPN to check, nothing else.
Unless it's illegal in your country, if it is, beware.
These mirrors work with HTTPS with valid certificates
https://ftp.lysator.liu.se/ubuntu/
https://mirrors.bloomu.edu/ubuntu/
https://mirrors.cs.wmich.edu/ubuntu/
These all work with HTTPS but have invalid certificates
https://mirrors.coopvgg.com.ar/ubuntu/
https://ubuntu.xfree.com.ar/ubuntu/
https://ftp.ccc.uba.ar/pub/linux/ubuntu/
https://ubuntu.unc.edu.ar/ubuntu/
https://mirror.aarnet.edu.au/pub/ubuntu/archive/
https://ftp.iinet.net.au/pub/ubuntu/
https://mirror.internode.on.net/pub/ubuntu/ubuntu/
https://mirror.overthewire.com.au/ubuntu/
https://ubuntu.mirror.uber.com.au/archive/
https://gd.tuwien.ac.at/opsys/linux/ubuntu/archive/
https://mirror.dhakacom.com/ubuntu/
https://ftp.byfly.by/ubuntu/
https://mirror.datacenter.by/ubuntu/
https://ftp.belnet.be/ubuntu.com/ubuntu/
https://gaosu.rave.org/ubuntu/
https://ubuntu.mirrors.skynet.be/ubuntu/
https://ubuntu.mirrors.skynet.be/pub/ubuntu.com/ubuntu/
https://archive.ubuntu.com.ba/ubuntu/
https://mirror.globo.com/ubuntu/archive/
https://ubuntu.ufba.br/ubuntu/
https://espelhos.edugraf.ufsc.br/ubuntu/
https://mirror.unesp.br/ubuntu/
https://sft.if.usp.br/ubuntu/
https://www.las.ic.unicamp.br/pub/ubuntu/
https://mirror.its.sfu.ca/mirror/ubuntu/
https://mirror.cpsc.ucalgary.ca/mirror/ubuntu.com/packages/
https://ubuntu.skarta.net/ubuntu/
https://ftp.iitm.ac.in/ubuntu/
https://biruni.upm.my/mirror/ubuntu/
https://cesium.di.uminho.pt/pub/ubuntu-archive/
https://ftp.rnl.ist.utl.pt/pub/ubuntu/archive/
https://free.nchc.org.tw/ubuntu/
https://mirror.umd.edu/ubuntu/
https://mirror.uoregon.edu/ubuntu/
https://www.club.cc.cmu.edu/pub/ubuntu/
https://mirror.clarkson.edu/ubuntu/
https://mirror.vcu.edu/pub/gnu+linux/ubuntu/
Along the lines of pwnguin's answer but if they are strictly blocking HTTP URL strings then simply using FTP or rsync should get you through the filter. Obviously they aren't inspecting connection content TOO closely or this post wouldn't have made out of the country in the first place since it contains the "p word"
Also, this kind of blocking is silly. But I suppose you already knew that.