People are concerned about Google should read
this.. So the article quotes Comcast as saying they don't sell your info - last time I talked to customer service, they said they needed my full SSN. I declined and the rep said she couldn't help me with my issue. I gave her bogus numbers I rattled off.
Not sure you can got to the web and "delete posts", but you can avoid targeted ads on your browser by using browsers like Firefox with adblock plus and NoScript addons installed. If you log onto Google to get your mail - log off when done. If you must use Facebook, figure out the privacy settings and use them. you can also configure Windows 10 not to spy on you.
You can also use a private browsing session on Internet Explorer.