Are premium channels censored in visuals or in words used?

From your description of what's going on, I strongly suspect the censorship is happening downstream of the provider.

Premium cable channels have very few regulations as to what they're allowed to air, at least in the US where most of them are based. Since they don't broadcast over the air, they don't fall under FCC jurisdiction. Typically they will stop short of anything overtly pornographic, but only just barely.

Even if you're not living in the US, this still impacts you, because it affects which movie cuts those channels license, and what kind of original content they produce. Cinemax, for example, is infamous for it's late-night softcore pornographic shows, and HBO airs Game of Thrones, which is chock full of nudity and swearing. They also have no issues airing the original theatrical releases of R-rated and NC-17 rated movies.

What's particularly odd about what you're describing are the censor bars being placed over the screen. Those kinds of artifacts typically show up when people want to censor material that they can't otherwise edit. But premium movie channels could choose not to include nudity in their original programs, and eventually most movies end up with a PG-13 cut suitable for broadcast TV that they could choose to air. There's no good reason for HOB or Showtime to throw censorship bars over a scene they chose to air in the first place.

I strongly suspect that something is intercepting the programming before you see it and doing that censoring, although I'm at a loss as to how they're doing it on the fly.

Some time ago, I asked HBO why an edited movie was aired on a pay channel. HBO admitted some movies ARE edited for content and/or visuals even though customers pay for premium viewing (no edits, cuts or censorship). The Reason (should we decide to accept): Movies are purchased in bundles. Apparently HBO doesn't know what movie they're getting. Not kidding! So, when the "exclusive-first-showing-out-of-the-theatres" film airs, HBO has "NO IDEA" what movie they're getting. Personally, it sounds like Placate The Customer 101. More viewers should complain. "Emmy King" or not, it'seems absolute crap ANY pay channel does/gets away with this! Case in point: just watched "Ride Along 2." Everything curse--songs included--was "muffled." Even a woman rinsing, in a thong bikini, butt-shot primary to camera, was "blurred." I only noticed the blur because without the...separation of her buttocks showing, the woman looked deformed. Absolutely ridiculous. TV'show changing. The pay-channels better take notice...