How to delete ad.doubleclick.net ?

You can try using these steps:

Force Quit Safari ( command + option + esc keys).Then restart Safari holding the Shift key. If you still have problems Empty Caches (Safari menu > Preferences > Privacy > Remove all website data. (This will also remove history if you do not want to remove History open Safari Preferences > Advanced and check mark “Show Develop Menu” then choose “Empty Caches” from Develop Menu ).

Then go to Safari Preferences > Extensions and check there. If there is an extension delete it.

https://www.2-spyware.com/remove-ad-doubleclick-net-ads.html#h-mac-os-x

https://www.2-spyware.com/remove-ad-doubleclick-net-ads.html#h-google-chrome

Download and run Malwarebytes. Malwarebytes was developed by one of our own colleagues here in ASC and is about the most proven anti-malware software for Mac.

Not sure about Chrome.