Some of Cameroon's neighbours, including Niger and Nigeria, have arrested leaders in Southern Cameroon and sent them back home. They are now in jail. Nigeria supports Cameroon in what it's doing because Nigeria needs the partnership with Cameroon to fight Boko Haram.
The Central African Republic has its own issues.
Chad, for its part, can't come out against Cameroon because it depends on Cameroon's resources. The pipeline is an obvious example.