Unable to figure out which ad network is responsible for pop-up ad

I’m facing serious problem. My site is: https://digitallnews.com
Using latest version of wordpress & theme: ColorMag By ThemeGrill.

Though i’m using many ad networks, but all of them are banner Ad.
But, for each new user(new IP) my site is showing pop-up Ad every day.

I really don’t like to use this pop-up ad showed in my site. As it’s helping to increase bounce rate for my site.

I have tried to disable almost all the Ads without no luck. I’m kind helpless & don’t have any clue how to remove this stupid culprit Ad network from my site.

As my site is build with wordpress, so i might curious to know, if anyone might show me way forward to fix this.