Q: it wont let me sign in with my apple id because someone else is stilled signed in to their account still

Is that your phone number?

The previous owner has to sign out and reset the phone to factory condition. Otherwise, the phone is useless to you. Try getting your money back, if possible.

What to do before selling or giving away your iPhone, iPad, or iPod touch - Apple Support

Hi

The person who use to own this iPhone needs to go to find my iPhone on an apple device they have

And remove iPhone from the list of devices .

Only then can you setup iPhone with your apple ID .

Have you just bought this iPhone second hand ?

Iff the seller can't do this get your money back .

Cheers

Brian