Registering the phone in an account would not cause any action on other phones you had.
If the system returns a message immediately after you enter the serial number that your request cannot be completed, that means the phone has been killed. If it says the serial number is not recognized by the system, that means it was not scanned at the retailer. That doesn't automatically mean the phone was not purchased legit.
It is possible that the phone is legit but a glitch somewhere caused the serial number to be missed for activation. I bought a phone and sent it to a customer and Trac would not activate it. They said it was not scanned at the store. I have the Walmart receipt with the phone's serial number on it showing the scan so I know it was.
Knowing exactly what message you receive when you try to activate would help some.
There's no present. There's only the immediate future and the recent past. –George Carlin