Why does my personal iPhone always say I'm using messages for business?

My iPhone is a personal device, but whenever I contact support it says I'm using messages for business and when I recently put the phone into lockdown mode, due to phishing texts, it says:

"Cannot use Messages for Business

Cannot use Messages for Business when device is locked down"

I always start support chats through the Apple support app and when I asked a support rep and they told me this and wouldn't explain further instead they "suggested" I start a new chat on the web???

"If you initiate a chat using messages app of your device, it will always come as Apple business chat.

If you initiate a chat with the help of the support app, it will show as web chat."