Advice re DNIE card and residencia

If you have a Spanish passport you are already a Spanish citizen, so will need to apply for your DNI but not for a residencia as these are for non-Spanish citizens. Whoever organised your Spanish passport should be able to tell you what your next steps should be.

I have been told I need both.

I believe what chrissy has told you is correct, if you have a Spanish passport you are a resident, how did you obtain the passport without a DNI?

My mother is Spanish

I had to apply for my DNI at the local police station in person. You'll probably have to go and make an appointment. You'll need your passport and passport photos for the DNI. There is a charge but from what I remember it's not much. As in, could be around 20euros, possibly less.

Many thanks