They should be placed in the following folders
For personal use
TTF files in ~/.local/share/fonts/truetype (old way was ~/.fonts/truetype)
OTF files in ~/.local/share/fonts/type1 (old way was ~/.fonts/type1)
For system wide use
TTF files in /usr/local/share/fonts/truetype
OTF files in /usr/local/share/fonts/type1
Then sudo fc-cache and you should see the fonts.
An alternative way is to place fonts generally in ~/.local/share/fonts/ (old way was ~/.fonts/).
Can you see the new fonts in Libre Office or similar office programs?
sudo fc-cache...?