If you are using the APN correctly, then there should be no additional charges from another provider. Please make sure that your APN setting has no spaces at either the front or the back and is set to ‘afrihost’. Please note that devices may differ in how their operating systems handle APN access.
Make sure that you check your device settings that it does not default to another APN setting. Certain actions, such as tethering your device as a wireless hotspot, can sometime result in defaulted APN settings.