If you have bought an Activation Locked Apple Watch, don't bother asking Apple for help. They won't help you in any way. They especially will NOT try to reach the previous owner for you. The ONLY person who can unlock the watch is the person who locked the watch. The fact you cannot reach the previous owner, likely means you bought a stolen Apple Watch. And that means you bought nice wrist ornament, which will NEVER function for you.
If you can't get the required help you need from the person who locked the watch, either try to get your money back and if that is not possible, recycle the watch responsibly and chalk this up to a bad buying decision.
Read this link about buying used devices --> The All Too Common SAD Reality of Buying … - Apple Community