Phone number being used by another account

I just got an iPhone 8 and transferred my SIM card successfully. My phone number used to be connected to my parent's apple ID, however I am trying to switch my phone number to my personal new ID. Even though I removed my phone # from my parent's ID and I don't see my phone number anywhere on their account, anytime I try to add my phone number to my new apple ID it says my number is being used by another account. How can I ensure my number is completely removed from my previous account?