Visitors location registered as United States of America


I am in the UK and have asked some people to visit our website from a particular country Nigeria. Many people have done so now. But when I checked piwik to see where the visitors are coming from, it show United States of America for all other visitors and shows United Kindgom for my own visits.

How can I correct this error and make is show the Nigerian visitors correctly, please?

I will appreciate your advice.