Why am I constantly getting 'ads by google' on phone and tablet?

[AC Question]

Last 3-4 days I've been getting ads on my samsung galaxy s4 and galaxy tab 8.4 pro all the time. Doesn't matter what app I'm using, I get those annoying ads sometimes full screen, sometimes tiny ones at the bottom of the screen. There's a little 'i' in the left lower corner of the ad, when I press it it says 'ads by Google'. I've opted out of interest based ads in Google settings but this hasn't changed anything. Is there a way to stop this?