Here are the Apple support pages that outline the Activation Lock - and the only mechanisms by which it can be turned off:
https://support.apple.com/en-us/HT201365
https://support.apple.com/en-gb/HT201441
As you will discover, unless you are the owner of the AppleID that was last used to activate the device, or unless you can secure the cooperation of the previous owner, you’ll not be able to defeat or bypass the Activation Lock. Without documentary evidence that you are the original owner (such as sales receipt showing the serial number), Apple won’t assist - and nobody here will be able to help you here:
If you communicating with the previous owner whose AppleID was previously used to activate the device, the linked information above will be useful to them to release the Activation Lock. If they have forgotten their AppleID or associated password, the credentials can be recovered:
https://iforgot.apple.com
To recover your credentials, they will need access to any one of the following:
- Their primary email address mailbox that corresponds with their AppleID
- Any of the secondary/recovery email addresses that should be configured for their AppleID account
- Any of the trusted telephone numbers (fixed line or Cellular/Mobile) that are associated with their AppleID
Unless the AppleID account has not been fully/correctly configured, or has been seriously neglected, recovery of the AppleID and password should not be difficult.
More information about recovery of the AppleID:
https://support.apple.com/en-us/HT201354
More information about recovery of the AppleID password:
https://support.apple.com/en-us/HT201487
I hope you find this information and guidance to be helpful in resolving your difficulties.