Ignoring extenuating circumstances, activation lock can be turned off only by entering the correct Apple ID/password combination. The correct combination is the one used in setting it up prior to erasure. Note that there is no way we can help you to systematically recover the pertinent Apple ID password.
If you have extenuating circumstances (e.g., you have the receipt for your purchase of the device with its serial
number on it or a court order instructing Apple to assist in the provision of access to a decedent’s information from the deceased person's accounts--(see How to request access to a deceased family member's Apple accounts https://support.apple.com/en-us/HT208510) If you have either, contact Apple support using one of these options, see if Apple support will help you with your activation lock problem you choice of support services:
Get a call from Apple support to help solve your problem using this link https://getsupport.apple.com/?caller=kbase&PGF=PGF63005&category_id=SC0245&symptom_id=23362
Apple ID Support https://support.apple.com/apple-id
Apple ID account security for country-specific and region-specific help https://support.apple.com/en-us/HT204169
Get Support: We’re here to help https://getsupport.apple.com/. Go through the options to find the best support option.