The Seller has not unlinked the phone from her iCloud. I cannot now contact her and Apple say it is unusable. Is there any way round this? I think not!
Hi Sever1ne! Welcome to iMore! Unfortunately, there's nothing you can do or Apple will do to remedy this situation. I'd continue to reach out to the seller though at some point that might become an exercise in futility. Sorry that this happened to you.
If you purchased second hand from a reputable site like swappa or maybe even eBay you may have some chance of retribution. If it was an in person cash transaction I'd advise that you ALWAYS require to be shown that there's no iCloud lock before money changes hands. If there's the slightest bit of hesitation take it as a scam and move on to the next seller.
Again, sorry that this happened to you.
Thank you so much. Eventually eBay refunded me