Why is my Spanish rice chewy?
I don't know that type of rice, but it sounds like it ran out of liquid before it was done. Some types of rice can be done in about 10m, some take over half an hour. My tricks for risotto like dishes are: 


wash the rice to remove loose starch
taste regularly so you can intervene as needed, 
avoid stirring as much as you can (you can stir a few times to avoid burning),
fry the rice with the onions before adding water,
add liquid in small batches until it's done.


Try it with a few small batches to get the hang of it. It could very well be the wrong type of rice, so you may want to try other brands.