Phone up to date, Carrier updated, says "Phone not allowed" in Network.

Hi all, I made a thread about two weeks ago but no updates.
My phone is an iPhone 6, running iOS 12.1. and Fizz 34.1
The phone is American, but fully unlocked, considering I used it with Public Mobile for a while, I also tested Telus and Rogers.
I tried getting help from Fizz themselves but they seem to say that they don't hold a list of blacklisted phones and such.
I know my phone is not blacklisted and IS unlocked, what could that mean ?
It just tells me "No Service" then this in the settings, despite fully working for a couple of seconds every single time.


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