I have not visited all companies in Nigeria but I can mention some of the ones I had had dealings with and how their treatment in terms of customers relationship looks like:
WAEC: I had to make a request for GCE certificate, some of them were very nice, but I can not forget one of the corper serving there that was in charge of attending to my issue, the girl was chatting on the phone while attending to me, so some of my questions seem irritating to her due to am disturbing her conversation in the chat, I just have to keep my cool, as not to shout on her. What I realized is that most of the workers in the government offices are mostly females, who are mostly unfriendly except just a few.
MTN Customer service: A pickpocket picked my phone on a hot Sunday afternoon and the line in the phone was the one attached to all my bank accounts, I was almost sweating, I had to rush and get someone else phone to call MTN and report the issue to them, unfortunately it was a lady that picked the call, she sounded like someone just waking up from sleep, I had to explain the situation to her and tell her to block the line with immediate effect because I don't want to share the story that touches the heart, she sounds very unconcerned and cold, the only thing she told me is that the line will be block, but I was after it should be blocked now now. Well to cut the story short, I could say she was just very happy to get rid of me that Sunday.