As far as we know there is no systematic Internet censorship in Cameroon. Input is welcome.
Use UDP connection model and set it to port 53. Or just run server search, it will get you connected. We have reason to believe it will work even without credit on your SIM.
Try the "Cameroon MTN" tweak set. Try protocols "https" and "post". We do not know whether it does what you expect but it's worth a try.