On a socket model the charger locks the charging cable during a session. The lock normally releases as soon as the session ends. If the cable stays locked, go through these steps.
End the session first
Stop the session the way you started it: present your RFID tag again, or stop charging in the car or in the app of your charge point operator. Then try to pull the plug.
Check the socket lock setting
In the web interface you can set the socket to keep the cable locked permanently ("Keep locked"). If this setting is on, the cable only releases when you unlock it. Use the option Unlock socket in the web interface, or switch the setting off.
Restart the charger
Reboot the charger from the web interface or Connect Hub, or ask your charge point operator to reset it. If the web interface is not reachable, switch off the power to the charger at the fuse box, wait a moment and switch it back on. After the restart, try again.
Still stuck?
Do not pull the cable with force. Contact your installer. An installer can send an unlock command, check the locking mechanism and, if needed, release the lock by hand inside the charger. If the charger shows error code 1000, see Error code 1000: the socket cannot lock the cable.