iPad Activation Lock Removal

Insofar as Apple is concerned, as someone else has associated the iPad with their AppleID, the iPad is no longer yours.

Unless you can prove to Apple's absolute satisfaction and discretion that you are the rightful owner of the iPad (this usually requires that you can produce the original purchase receipt that shows the device serial number), Apple will not release the Activation Lock. Apple will not become involved with disputed ownership - and this is likely to explain the rejection that you have received. The Activation Lock is applied on Apple's back-end security servers and cannot be bypassed; nobody but Apple can help you.

Regrettably, you have been scammed - and have no lost access to, and use of, the iPad. As a point of learning, never allow someone that don't explicitly trust to sign-in to their own AppleID from a device that you own.

The more convincing the documentary evidence that you can provide, the more likely you are to be successful.

At the end of the day, if Apple decline to release the Activation Lock, there is nothing that you can do to change the decision. Travelling to another country to make representation in person is very unlikely to alter the outcome.

I have not seen anything here on this support site other than the original purchase receipt from Apple or Authorized Apple Seller to prove ownership, but good luck!

It is rather easy to print out a receipt that would not prove ownership and also WhatsApp messages between 2 parties may not be sufficient. Just be prepared for this to be a learning lesson to never do that again.