i can't get my extension done as a nigerian

Note that the Legal Section at Jawabkom website only provides legal consultations, and doesn't have any relation with any entity whether governmental or nongovernmental.
In regard to preventing Nigerian citizens from extending the visa is a matter subject to the administrative decisions organized by the UAE government which did not announce a clear reason for this ban.
You can contact the General Administration of Residence in order to find out the reason for this via the link: