Deregistering imessage when my number "isn't registered"
Until a few days ago, I was using an iPhone 4. It completely stopped working on me, and I can no longer even turn it on. So, I switched to a Samsung Galaxy S6 Edge and just put it in the sim card today to start using it.
Now, I am able to receive messages from individual iPhone users, but I am unable to receive any messages in group chats since those messages are sent as iMessages. I realized that I needed to deregister my phone from iMessage, so I used the link: https://selfsolve.apple.com/deregister-imessage since I no longer had access to my iPhone to deregister it through Settings.
I put in my phone number, got the code, and put in the code. Then, I got an error message saying that my number "isn't registered with iMessage." What do I do? I need to be able to get group messages from people, but it isn't working. If my phone isn't registered with iMessage, how are people sending me iMessages right now? Any help would be much appreciated.
iPhone 4