There are a lot of advertising networks that resell adsense ads. Without applying for adsense, your site will be running adsense. I have tried infolinks and media.net in the past and these are adsense reseller. By using these ads, my site was basically running AdSense ads. There are also other companies that resell adsense ads, for instance, Ezoic, Mediavine etc. have you used any AdSense reseller ad networks on your site?