I previously bought a bronze package for 3 computers
There is no such thing. There are only licenses.
Now, as part of my PAID subscription, SafePrice browser highjacker has been installed.
Totally wrong! SafePrice is not malware at all. It is just a option that avast is offering you and you have the choice to install it or not. If you have installed it and decided you don't want it, just remove it.
The only way I can get rid of it is remove AVAST completely
Totally wrong again! It is just a module that you can install/remove without having to remove avast completely. Control panel > software > avast > change
And, of course I will not be paying again so that you can add unwanted extensions to my browser.
avast didn't do that. It was your own choice to install it. You could have chosen not to install it.
CUT IT OUT!!!! SHOW YOUR CUSTOMERS SOME RESPECT!!!!!
avast is showing the users a lot of respect, but as I said.. It was your own choice to install it. I strongly suggest next time you are trying to install something to use the custom install and read/do research before installing and not simply download something and just click next.. next... during a installation.
but did not prevent them from coming back
If they came back it is you as user that did not setup the security correctly.