TalkTalk are a completely awful ISP. Not sure what the US equivalent would be, but they're the kind who do promotions of "Broadband for £3/month"-level. You get what you pay for service-wise, but they are also by far the most enthusiastic ISP around when it comes to censorship; they have a spider that follows their users to all URLs they visit to categorise the sites[1] (giving them the nickname StalkStalk), and have been doing this long before the current set of idiots in Parliament forced censorship in (at least since 2011).

I'm in a similar situation, one site I run is blocked both by StalkStalk and BT. No porn, no other 'adult' content; it's deliberately kept PG-13 to use the US ratings.

[1]Check your logs for HuaweiSymantecSpider. It obeys robots.txt though, so a quick "Disallow: /" in robots.txt stops it, although they still grab content from unencrypted pages via DPI.