Redirects To Adult Porn Sites

I hope this is in the correct category, I don't know what to do about this continuous problem.

I have tried Mac Scan and deleted tracking cookies, but still periodically when I am surfing, I keep getting redirected to
adult Friendfinder site which has porn on it.

I have tried different browsers, but have the same problem on Chrome, Firefox and Safari

If I block this site on the router will it make any difference?

How do I stop these redirects

I use a Mac

Thanks for any assistance on this matter.