Hey L TIATOM,
It looks like you have a problem with the interior door handle.
You will need to remove the door trim and inspect the lock cable to the interior door handle.
I have attached instructions on how to remove a door panel on a Hyundai accent it should be the same/similar. Try googling Hyundai i20 door panel removal.
With all the screws removed the panel should pull off, the panel clips do require some effort to release.
With the door panel off actuate the lock and watch the operation of the handle cable.
Check the interior door handle moves freely.
Check the routing of the cable, it could be getting pinched if incorrectly routed.
I would say it is likely you need to replace the interior door handle/cable.
Any further questions do not hesitate.
Regards, Joe
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Monday, April 1st, 2019 AT 9:21 AM