after a call exhausted credits, the next call will fail with a timeout. found out it gets stuck in cnxcc_mod.c line 1137
static call_t *__alloc_new_call_by_money(credit_data_t *credit_data, struct sip_msg *msg,
double credit, double cost_per_second, int initial_pulse, int final_pulse) {
call_t *call = NULL;
lock_get(&credit_data->lock);
... the next lines will never be executed