My iphone stopped working after 15 days.

Hey everyone, so I purchased a iphone 13 pro (global). I asked the shopkeeper whether I will face any problem because of the global varient he said no, I askedif the phone's new he said yes and I opened the seal. there was 'no warranty' on the phone

After 15 days it turned off automatically when I turned it on it showed battery not genuine and charge was stuck at 1% I gave it tohim he took the phone and said we'll look into the matter whatever will happen.

He keeps on saying tomorrow I will give your phone it's in parcel not yet arrived blah blah excuses, what I think he will do is change the battery that too not genuine

What can I do I don't want that phone as I paid for new and what if he says there's nothing I can do and there was no warranty