Q: Bought an iPhone 6s   With activation lock. No way to contact seller either.

Since there is no way around Activation Lock, you need to return it and get your money back if possible.

There is no way to bypass Activation Lock.

You need the Apple ID and password used to lock it to remove activation lock.

Failing that, you would need to produce a valid purchase receipt from Apple or an authorized reseller for Apple to be able to help you.

Otherwise, your only  choice is to return it to wherever you bought it from and demand a refund, it is useless to you, and should not have been sold.