iPhone is not activating after recovery

Hello,

I buy an refurbished iPhone 6s plus on eBay, from France.

The phone was not working at delivery time, so I contact the seller and ask for help: he told me to connect it to the latest iTunes version and the program will do a clean recovery of the iPhone, which will make the refurbished iPhone as a new one, then I will configure it at my name, add it to my iCloud, etc.

After doing these steps, which worked as the seller describe it, I set my language and country, an WiFi network and then it demands an iCloud account which I do not know. If I make mine, it does'nt work.

The seller said that I must walk at an Apple Service Point and they will unlock it for me.

Is this true? If so, where do I must walk? What happens if the iCloud account demanded is from a previous user, which lock it because it was stolen or lost?

Thank you in advance for your answers and advice.