Locked, Blocked... or Not? You tell me?

I am wondering if anyone else has ever had a sim suspended after installing it in a used iPhone. Because the first one I bought worked for a day before I got a recording saying the device was blocked from activation. Red Pocket Mobile confirmed it had been listed as lost or stolen. But what they couldn't tell me was why I was able to activate it in the first place? They activated it a second time with the same results. So I pulled the sim and had them activate one more time so I could at least pay the bill and keep the line active while I searched for another phone.

Fast forward to today when the second one arrived and did the same thing as soon as I inserted the sim. That's strange. Not because two used iPhone's from eBay were reported lost or stolen but because they were two used iPhones that allowed me to sign in with my Apple ID, list in my iCloud as Trusted Devices and even receive the authentication code text to sign in on my desktop!

When I called the carrier again today they confirmed my sim was suspended again for inserting it in phone listed as lost or stolen. This time I sent them the clean background checks on the phone and another after I turned Find My off. Then he began to agree with me, it's kind of strange. After putting me on hold for a 1/2 hour I re-inserted the sim and restarted the phone and he said if it happens again send the phone back. And I will, except I only have 3 days to complete the transaction.

So i guess my question is... does this happen often or can it even happen at all? It can't be possible to use my Apple ID to log into a device that has been claimed lost or stolen, can it? I would be impossible to take control of a devices Find My, right? The phone is neither carrier lock nor is it black listed but my sim card seems to think different.

Also, I realize there is a big difference between locked and blocked. And I get that a used phone is at risk to be blacklisted well into the future but I would think the carrier sim lock info on the phone is pretty accurate. If so, the phone would obviously be paid off and the only reason for a future black list would be turned in lost or stolen by a previous owner. Could this still happen after a new owner has taken full ownership of the phone? Can the same phone be registered as a Trusted Device under 2 different accounts?

I am not an idiot and believe that if you want something done right, you do it yourself. But I am also the first to admit when I am lost. Any help would be appreciated. Thanks, Paul