ExternalServiceUpdateAccount.cls

//update account
ExternalService.BankService service = new ExternalService.BankService();

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

req.accountName ='GreenMotorCorporation';
req.accountType = 'Customer';
try{
    //make callout
    ExternalService.BankService.updateAccount_Response res = service.updateAccount(req);
    system.debug('200 response id => '+ res.Code200.id);
    system.debug('200 repsonse: name => '+res.Code200.name);
    system.debug('200 repsonse: available balance => '+res.Code200.availableBal);
    system.debug('200 repsonse: type => '+res.Code200.z0type);

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