Open a terminal and enter "inxi -Gx" If it's installed correctly you should see your card identified by the model number. See the attached pic for a correctly installed and working RX 470. You can also just look in System Info and it should be listed there (I'm using Linux Mint, based on Ubuntu 16.04 - based on my recollection of when I have used Ubuntu, I believe it would be the same.). If it identifies the graphics card with some code number other than the model of your card (which you should list) it's not. Without more details it's hard to say what your problem is, but a couple things I would check:
What kernel version are you using? Ubuntu 16.04 used 4.4 and these drivers seem to need 4.8 or 4.10.
Do you need to remove old xorg configuration?
The bottom of the second page of this thread https://forums.linuxmint.com/viewtopic.php?f=59&t=229229&start=20 has a walkthrough of my installation procedure in Linux Mint 18.1. It should be the same for you except you don't need to modify the install script and you should use gedit or other preferred text editor instead of xed.
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