How to use an Injectable Service in a custom Validator

I have this Scenario:-

I am creating a customvalidator in my app which uses a service to get Data

import { AbstractControl } from '@angular/forms';
import { IndianStatesAndCitiesService } from './indianstatesandcities.service';
export function SpecificState(control: AbstractControl) {
    let iss : IndianStatesAndCitiesService;
    let getiss : string[] = [];
    for(let i in iss.getStatesAndCities()){
        getiss.push(i);
    }
    if (control.value !== undefined && (getiss.includes(control.value))) {
        return { 'specificState': true };
    }
    return null;
}

But it is throwing following Error:-

ERROR TypeError: Cannot read property 'getStatesAndCities' of undefined
    at SpecificState (specificstate.validator.ts:6)

Is there anyway i could use the angular service inside that function??

replace this

let iss : IndianStatesAndCitiesService;

with

var iss = new IndianStatesAndCitiesService();

you haven't created an object of service try this