enforce unique values in 2 columns javascript

I have a sharepoint list and I want to enforce unique values in a people picker and a dropdown column

so I created a JS and in the PreSaveAction function, I call a function CheckExists() and that function calls the REST API and check if there is an existing value in my list.

I have this code

function PreSaveAction() {
    if(CheckExists())
        form.SubmitClientForm();
    else
        alert('employee and tp exists!!!');
}

function CheckExists() {
    var OCFormEmpNameSid = $("[id^='Employee_x0020_Name'][resolveduser='true']").attr("sid");
    var OCFormTpNo = $("select[id^='Tp_x0020_No'] option:selected").text();
    var listUrl = _spPageContextInfo.webAbsoluteUrl + "/_api/web/lists/GetByTitle('my list')/items?$select=*,Employee_x0020_Name/Name,Tp_x0020_No/Title&$expand=Employee_x0020_Name,Tp_x0020_No/Title";
    var c = null;
    $.ajax({
        url: listUrl,
        type: "GET",
        headers: {"Accept":"application/json;odata=verbose"},
        success: function (data) {
            $.each(data.d.results, function(i, item) {
                var listEmpName = item["Employee_x0020_Name"].Name;
                var listTp = item["Tp_x0020_No"].Title;
                if(listEmpName != undefined) {
                    if(OCFormEmpNameSid === listEmpName && OCFormTpNo === listTp) {
                        c = true;
                        return false;            
                    }                                                       
                }
            });//each
            return c;
        }
    });

the code above always says that the employee and tp exists.

I also tried different methods without using the PreSaveAction method but it still saves the item even if there are duplicates