I said "sounds like" after quickly looking over Glasswire's and Anti-Beacon's features list/description. You didn't mention how you knew it was blocking telemetry in your original post.
Although I'm still curious exactly what is being blocked from your ISP being able to see. For example, unless you've manually configured your DNS settings (or Glasswire configured them for you), you're probably using your ISP's DNS, meaning they can in theory see every site you visit. And if you DNS has been changed, then that just means that some other DNS provider can see which sites you visit.
Even though someone in the sales department can no longer see whatever subset of your information they normally can, I don't think that guarantees all your browsing information is being blocked from the ISP. To be honest, I don't think that's even possible to do solely with software/settings on your local PC.