How to reset apple ID

Hello, I recently bought an iphone 5s, I tried copying contact into it from an older Nokia phone, and during copying, it somehow copied some strange apple ID from different country, without asking for password or anything, now the account is in the device without the possibility to reset.

I have proof of purchase with serial/imei, and all other documents, that device belongs to me,is there any possibility to reset the device completely? I tried contacting the service center, but they ignored me.

I tried contacting the strange person, whose apple id appeared in the device without luck, do I have any other options?

Thanks