Multiple iPhones stuck in Activation Lock.

Your only option is to submit a request to remove the Activation Lock. This will require the original purchase receipt from Apple or Authorized Apple seller to remove the lock.

How to remove Activation Lock - Apple Support

It is a tough lesson to learn, but the devices are now locked to someone else and you are forced to prove the devices are actually yours and the only way to do that is the original purchase receipt. Nothing else will be accepted.

● Apple might reset a device if you can prove to Apple's satisfaction you are the owner. However, they will not do so if Lost Mode is set on a device such as may have been done if you fell victim to a scam where you signed into your device with a different account.

Apple can completely reset a device if a person can provide sufficient evidence of valid ownership. This is done online* at: Activation Lock support request - https://al-support.apple.com/#/additional-support Apple says, "Proof of ownership documentation is required," but does not provide many details in the article as to what is acceptable proof. Prior to this official service Apple typically required the original receipt** issued by Apple or an Apple Authorized Reseller. Note that while this will let you get use of the device again, it will not help you with lost access to an account.

* There is a special link for this service. To save time you should use it instead of https://getsupport.apple.com/

**Apple recommends you keep your receipt after you buy an Apple device. --> Keep your receipt after you buy an Apple device - Apple Support

Akveleon wrote:

If there is no receipt but there is an original box, can I throw away the phone? The phone was brought to Russia from India through a parallel import, and was sold already activated.

Original box will not help. Instead of adding to the landfill, it is best to give it to a recycler if one is available.