Did you or someone else erase your device without signing out of iCloud first? If so, that may be why your phone is activation locked. You can turn activation lock off only by entering the correct Apple ID/password combination. Note that the correct Apple ID/password combination is the combination allowed by the person owning the device. If this combination cannot be entered, then the phone is useless to you unless there are 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.
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.