Who I have the same questioned this topic

I activated a Samsung S21 Ultra, but the old Pixel 2XL is still receiving text messages.  I will note that when I activated the new phone I did not know the old phone had to be turned off, so it was left on.  Afterward I did turn off the old phone and turn the new one off and on again, but when I turned on the old phone again to see if that worked it was still receiving texts.  How can I fix this?