We consider the problem of dynamic bandwidth allocation among different service classes under uncertainty in cognitive radio networks. In such networks, the secondary users compete for bandwidth resources and the service providers compete for users access (e. g., subscription). To address this problem, a two-level dynamic game framework is developed. The underlying dynamic service selection of secondary users is modeled as an evolutionary game based on replicator dynamics. The randomly irrational churning behavior of secondary users is modeled as a stochastic disturbance to the service selection distribution evolution. At the upper level, a bandwidth allocation stochastic differential game is formulated to model the competition among different service providers. The service selection distribution of the underlying evolutionary game describes the state of the upper stochastic differential game and a Markov perfect Nash equilibrium is considered to be the solution. The decentralized nature of the framework makes the system flexible and simple for implementation.