It is very sad indeed that you, as an African, was not accepted by the volunteer organisation you approached.
Why not post the name of the organisation on this forum board to make others aware.
I feel that so many people are setting up as volunteer organisations because they are in it to make money rather than actually provide help to the people in need.
They could have refused you because, as an African, you will be aware of the actual costs of their works and how much they charge in fees to volunteers and then you would be in a position expose them as profit being their motivation.
If is very difficult to know which organisations advertising for volunteers on this forum board are genuine and which are not.
General rule would be: it is normal for them to charge a SMALL fee for food and accommodation but if they are charging high fees, they are more likely to have profit as their main goal, rather than helping the people who need it.