Removing subinterfaces from interfaces file brings them back upon reboot

[sdewan]

I am not very experienced with ubuntu and trying to remove some subinterfaces within ubuntu. However, every time I remove the subinterfaces by running "sudo nano /etc/network/interfaces" command, these interfaces come right back.
Ubuntu version: 12.04.5 LTS
Then, I found this command "IP link show" which showed that these interfaces are in UP state. So, I ran "sugo ifconfig eth.300 down" to bring these links down.
However, everytime I restart my ubuntu server, all the subinterfaces I've deleted come back.
How can we permanently delete these sub interfaces?

[wildmanne39]

Please use the default font color and properties unless you need to highlight or draw attention to a part of your post.

[guiverc]

Ubuntu 12.04 LTS is EOL (http://fridge.ubuntu.com/2017/05/01/...april-28-2017/); being released in 2012-April (thus 12.04) with 5 years of supported life.

If you're using Ubuntu 12.04 ESM, I'd suggest using your Ubuntu Advantage support options, otherwise I'd suggest you move to a supported release of Ubuntu.

The normal release-upgrade path for 12.04 upgrades is to 14.04 LTS; however it's also now EOL; so a re-install may be necessary.

Ubuntu LTS releases come with 5 years of support; so 12.04 was supported until 17.04 (or 2017-April) unless extended using ESM.