It might be helpful to check at night, after dark, with a flashlight. Things like vine weevils and slugs might be around. Also take the inner pot out and examine underneath, including the drain hole. If you can lift the root ball out of the inner pot intact have a look there too. Any grubs? The edges of the damage look healed, so it is possible the creature that did it has gone. Is it still happening?

Thank u for suggestions. I will check. It is still happening unfortunately.

No, you should never use Orthene inside the home. Follow floral’s advice and find the critter in person. You can also try putting the pot into another vessel, even the sink, and submerge it in tepid water for a few moments. If something is hiding in the soil during the day, it is likely to come out when flooded.

Appreciate your advice and advice of Floral UK. Good idea to soak the plant. I can always put in more soil.