There is a activation lock on an iPhone I got from eBay

Neither we nor Apple can help you. Activation Lock its an anti-theft feature and only the previous owner can remove the lock. If the previous can not or will not remove the lock, then the device is useless to you or anyone else. Apple will not help you find the previous owner. Try to get a refund (through eBay) or dispose of the device properly. Sorry. For more info, see:

How to remove Activation Lock - Apple Support

What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support

There is no known way to bypass activation lock without the assistance of the previous owner. If you you cannot contact the previous owner, see if you can get a refund through ebay: https://pages.ebay.com/ebay-money-back-guarantee/