Some cars have a safety feature apart from normal fuel cap. Inside the tube to tank , there is a spring loaded flapper. Purpose of this flapper is to prevent fuel coming out of tank in case of accident and vehicle is upside down.

When you go for refuelling again, ensure that filling nozzle is inserted deep inside. This will prevent accidential cut-off of filling due to closure of internal flapper.

Still it is not working, then ask Hyumdai Motors.