ExternalServiceCallout.cls

//Call external services registered actions from apex
//Instantiate the external service Apex class

ExternalService.BankService service = new ExternalService.BankService();

//set request
ExternalService.BankService.getAccount_Request req = new ExternalService.BankService.getAccount_Request();

req.accountName = 'DynamicsCorporation';

try{
    //make callout
    ExternalService.BankService.getAccount_Response res = service.getAccount(req);
    system.debug('200 response id => '+ res.Code200.Id);
    system.debug('200 repsonse: available balance => '+res.code200.availableBal);

}catch(ExternalService.BankService.getAccount_ResponseException exc){
    system.debug('404 response: error message => '+ exc.code404.errorMessage);
}