MS Dynamics CRM 2016 Online Javascript Error

Hi I have applied below javascript code on change of "Account Name" field of contact entity but I ma facing below error message on change of Account Name field.

One of the scripts for this record has caused an error. For more details, download the log file.
ReferenceError: OnAttributeChangeParentCustomer is not defined at eval (eval at RunHandlerInternal (nestleeurope.crm8.dynamics.com/.../ClientApiWrapper.aspx), <anonymous>:1:1)

Javascript code is as below :

function OnAttributeChangeParentCustomer(){
var parentCustomerLookup = Xrm.Page.getAttribute("parentcustomerid").getValue();

if (parentCustomerLookup == null) {
var deleteAddress = confirm("You have deleted the Parent Customer from this contact record. Do you want to delete the contact's address as well?");
if (deleteAddress == true){
this.UserConfirmsToDeleteAddress();
}
}

if (parentCustomerLookup != null && parentCustomerLookup[0].entityType == "account") {
var accountId = parentCustomerLookup[0].id;
var accountName = parentCustomerLookup[0].name;
var copyAddress = confirm("If parent account \"" + accountName + "\" has address information, do you want to overwrite this contact address with account address?");
if (copyAddress == true) {
this.UserConfirmsToCopyAddress(accountId);
}
}

},

----------------------------User confirms to delete address---------------------------------

function UserConfirmsToDeleteAddress(){

//Delete contact address information
Xrm.Page.getAttribute("address1_city").setValue(null);
Xrm.Page.getAttribute("address1_country").setValue(null);
Xrm.Page.getAttribute("address1_line1").setValue(null);
Xrm.Page.getAttribute("address1_line2").setValue(null);
Xrm.Page.getAttribute("address1_line3").setValue(null);
Xrm.Page.getAttribute("address1_stateorprovince").setValue(null);
Xrm.Page.getAttribute("address1_postalcode").setValue(null);

//Saves the record synchronously
Xrm.Page.data.entity.save();
},

------------------User confirms to copy address-------------------------------

function GetAccount(accountId, successCallback, errorCallback) {

//OData URI to get address information from parent account record
var oDataURI = Xrm.Page.context.getClientUrl()
+ "/XRMServices/2011/OrganizationData.svc/"
+ "AccountSet(guid'" + accountId + "')"
+ "?$select="
+ "Address1_City,"
+ "Address1_Country,"
+ "Address1_Line1,"
+ "Address1_Line2,"
+ "Address1_Line3,"
+ "Address1_StateOrProvince,"
+ "Address1_PostalCode";

//Asynchronous XMLHttpRequest to retrieve account record
var req = new XMLHttpRequest();
req.open("GET", encodeURI(oDataURI), true);
req.setRequestHeader("Accept", "application/json");
req.setRequestHeader("Content-Type", "application/json; charset=utf-8");
req.onreadystatechange = function () {
//debugger;
if (this.readyState == 4 /* complete */) {
req.onreadystatechange = null; //avoids memory leaks
if (this.status == 200) {
//parse the response string as a JSON object into the successCallback method.
successCallback(JSON.parse(this.responseText).d);
}
else {
errorCallback(accountId);
}
}
};
req.send();
},

function CopyAccountAddressToContactAddress(account) {

//Set contact address information
Xrm.Page.getAttribute("address1_city").setValue(account.Address1_City);
Xrm.Page.getAttribute("address1_country").setValue(account.Address1_Country);
Xrm.Page.getAttribute("address1_line1").setValue(account.Address1_Line1);
Xrm.Page.getAttribute("address1_line2").setValue(account.Address1_Line2);
Xrm.Page.getAttribute("address1_line3").setValue(account.Address1_Line3);
Xrm.Page.getAttribute("address1_stateorprovince").setValue(account.Address1_StateOrProvince);
Xrm.Page.getAttribute("address1_postalcode").setValue(account.Address1_PostalCode);

//Saves the contact record asynchronously with callback methods.
Xrm.Page.data.save().then(
function () {
var msg2 = "Successfully copied and saved contact record.";
//display a non-blocking alert dialog
Xrm.Utility.alertDialog(msg2, function () { });
},
function () {
var msg3 = "PT.Contact_Main.CopyAccountAddressToContactAddress Error: Cannot save contact form with new parent account informatin. Please check contact and account records.";
//display a non-blocking alert dialog
Xrm.Utility.alertDialog(msg3, function () { });
}
);
},

function GetAccountErrorCallback(id){

var msg1 = "PT.Contact_Main.GetAccount() Error: unable to retrieve account record with accountId = " + id + ".";
//display a non-blocking alert dialog
Xrm.Utility.alertDialog(msg1, function(){});

},