I dont know what you did … but it appears you did it wrong.
Also … without some extra work, you cant ‘not use the amd driver’ … its opensource and in the kernel.
And I really dont think you want to be using VESA or some other ‘generic’.
Hm… by the above did you mean you tried to forcibly install Catalyst? If so … dont do that.
I guess I will leave the following in case your issue is as simple as booting and force reinstalling the drivers (probably after removing anything extra you did, and doing a full update - sudo pacman-mirrors -g && sudo pacman -Syyu)
[HowTo] Resolve an unbootable Manjaro (black screen, login failed, cant boot, etc)
Configure Graphics Cards - Manjaro