Called about scheduling a maintenance on my "cooling unit". Does not apply to me, I asked to be removed from thier list and then they hung up. Blocked.

Have  called  number of times. Won't  say anything very annoying.

Calls several times a day. Never says anything.  When number is called back message says that call cannot be completed as dialed.  Cannot even block this number. calls says number is invalid

The reason your call blocker says this number is invalid is because of the "811" in the exchange part - there are no such exchanges anywhere in the USA or Canada. This number is a spoof number, the scammers don't want people calling them back.

You don't say what you are using to block numbers.
If it is your TSP (Telephone Service Provider) notify them that this "impossible number" has to be blocked.
If it is call-blocking equipment for your landline, look to see if specific exchange numbers can be blocked.
    Or you might have to get newer equipment.
If it is an app on your smartphone, the app needs to be updated or get a better app.

Illegal spoofed call, and illegal spoofed call = SCAM.  Didn't answer (I NEVER answer calls from unfamiliar numbers).  Blocked this number.