Fnb network is robbing people

I have port my vodacom number to fnb network and since last week we have been trying to port it back to vodacom network Fnb is declining it and I don't know why I they declining as we never sign any contract that bind me not to port it back. This is violating my rights as to forcing me to use their network wich is not suitable for me anymore. Fnb bank is robbing me.