Deregister Nigerian number

Hopefully they can help you, click here for more support and assistance .

Or get support -> Apple Stores In Nigeria And Their Contacts Address: 

https://gmposts.com/apple-stores-in-nigeria-and-their-contacts-address/

Are you talking about deregister iMessage?

If so, see this Apple article: Deregister iMessage on your iPhone or online

Deregister iMessage on your iPhone or online – Apple Support (UK)