Discovery Visa Credit Card non-acceptance at Nigerian Banks and POS

I recently visited Nigeria with my Discovery Black Visa Card. The service from this card and Visa was appalling. I cannot describe in words at how many ATMs and POS did my card fail for no apparent reason. Banks and ATMs displaying the Visa sign. My card would work the one minute at a POS and literally a minute afterwards fail. I'm sure Discovery's ***** engine went haywire in the background. I've spent hours chasing different banks ATMs to get money. Discovery really need to have a chat with Visa to ensure their clients are adequately covered in Nigeria.