You cannot use this watch. You've very likely been scammed and unless whoever originally set up the watch removes the watch from their account, you are now the proud owner of a useless Apple Watch. Apple will NOT help you. We cannot help you.
You really got taken on this deal. Apple Watch Series 3, even in pristine condition was released over 5 years ago and is not worth $150. You could have purchased a brand new Apple Watch SE from Apple which is the latest watch for $249. If you can get your money back do so. If you can't, chalk this up to a bad buying decision and recycle the watch responsibly.
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