Apple ID account

Activation Lock Problem

If you purchased the device second-hand, then it is useless without the Apple ID and password to which it is locked. If you don't have it, can't remember it or cannot get it, then the device is useless to you. Try to get your money refunded, if you can, or take it to an Apple store for an exchange provided they will help you. If you are the original owner, then take the device, a copy of your purchase receipt and identity proof to an Apple retailer where they may be able to assist you. For a deceased owner, you will need a certified copy of the Death Certificate, the device, proof of inheritance and proof of your identity. Take all to your local Apple Store for help. Note: there is no guarantee that anyone can gain access to the device.

About Activation Lock on your Mac - Apple Support

Activation Lock - Turn off Find My iPhone

About Activation Lock on your Apple Watch - Apple Support.

Did they change your Apple ID or did they sign out of your Apple ID and sign in with their ID? If they signed in with their ID, ask them to sign out.