Brand new modem agent said they could not activate it because it was registered under another account.

so I tried my Internet and it turned out since my Home is fiber, optics, and no other modem router work for they told me so I went to they gave me a different modem, came home to activate it, and they were unable to say that they had to have an agent come out went over there another one told me the same thing that they weren’t able to activate it so I went and bought a brand new one, and when I had the agent activate it, she told me that she was unable to because it was registered to another account. how can that be if it’s a brand new product from target