I think I may be onto something, as I am having the same issue and I deleted the couple of apps I had downloaded to no avail.
Does the ad cover your screen when you go to answer a call or check a text? NOT in a browser?
You can't back out of the ad or pull up home, it just blocks access to everything until you X it out?
Often, the X's to close the ad still download some app or game?
There is no app listed that is obvious, no apps with obvious permissions, either.
But FINALLY I just found what is probably the culprit, by viewing Settings> Data Usage and there it was, ad_surface with almost 600mb of data this month and I don't browse or do much with my phone, mostly text and use for calls when I am out.
When I touch the app, the "APP SETTINGS" button is grayed out and useless.
I can also find it under Settings> Apps> Touch the 3 vertical dots> Show System and there it is. I am able to DISABLE it there.
I can't find it anywhere that I am able to delete it, so disable is all I can do now and I would like to know if anyone can tell me more about this and how to get rid of it for good (and where it came from!).
I am really shocked that searching for ad_surface yields no results.
I am including a couple of screenshots of the app.
Thanks for your help in advance.