Eu tenho duas aulasChargeCustomer eTwelvethViewController. No TwelvethViewController, tenho umfunc goNextView() que deve executar um segue para o próximo controlador de exibição quando chamado.goNextView() é chamado declass ChargeCustomer dentro de um manipulador de conclusão Alamofire. O problema é que essa funçãogoNextView() nunca é chamado e não consigo entender o porquê. Eu tentei fazê-lo funcionar com base nesta resposta no stackoverflowExecutar Segue de outro arquivo Swift através de uma função de classe

 class TwelvethViewController:UIViewController {

  //when this func is called, it should segue to Thiretheen
  func goNextView() {
    performSegue(withIdentifier: "twelvethToThiretheen", sender: self)
      }
 }

 class ChargeCustomer {

    //send a post request to the server
    Alamofire.request(urlString, method: .post, parameters: params, encoding: JSONEncoding.default, headers: ["Content-Type":"application/json"]).responseJSON {
        (response: DataResponse<Any>) in
                print("received reply from ALamofire") //prints string

           //perform segue to Thireteen View Controller
        func showNextView(fromViewController:TwelvethViewController) {
              print("went through")      //doesn't print
                 fromViewController.goNextView()
                    print("it has segued")      //doesn't print
           }      
      } ///end of Alamofire
   } //end of chargeUsingCustomer

Resposta atualizada de acordo com José Neto

 class ChargeCustomer {
 //create instance of the viewcontroller that has segue with identifier    twelvethToThiretheen
   let twelvethVC = TwelvethViewController()

    //send a post request to the server
    Alamofire.request(urlString, method: .post, parameters: params, encoding: JSONEncoding.default, headers: ["Content-Type":"application/json"]).responseJSON {
        (response: DataResponse<Any>) in
                print("received reply from ALamofire") //prints string

//perform segue to Thirteen View Controller
   //crashes: <CleaningApp.TwelvethViewController: 0x7fd4e16ad2a0>) has no 
     //segue with identifier 'twelvethToThiretheen''
 self.showNextView(fromViewController: self.twelvethVC )
      } //end of Alamofire

    //perform segue to Thireteen View Controller
   func showNextView(fromViewController:TwelvethViewController) {
        fromViewController.goNextView()      
       }      
} //end of chargeUsingCustomer