Regular utility easements are so dead common they wouldn’t need to be explicitly listed in the purchase and sale. It’s on the buyer to do their own due diligence as concerns easements. It sounds like the OP didn’t even pay for a real title search, or if they did didn’t understand it…

The county handles the registry of deeds, which is where any recorded easement would be. Suffolk County Registry of Deeds is searchable online. I would be fairly shocked if there wasn’t a utility easement that Comcast is entitled to use. I also think you’re being shortsighted, those easements normally require them to put the yard back the way they found it as long as you haven’t built, like, an in ground pool in the way.