I bought an iPhone and it has activation lock what do I do because I am unable to contact the seller

You most likely bought a stolen device and the seller is intentionally not responding.

Without the Apple ID and password it's asking for, the phone will be forever useless.

If this was a Craig's List or other user-to-user type transaction, you have no recourse. If this was through eBay, you may be able to file a claim for a fraudulent seller and possibly be reimbursed.

Your iPhone will make an attractive bookend or doorstop.

It was very likely stolen before you purchased it.

Get a refund if possible. The iPhone will remain useless forever.

If you can't get your money back, turn it over to the police.