This mattress is definitely not extra firm. I would say it's medium firm which is not what I wanted at all. There's a reason why someone would buy a mattress labeled as extra firm.
I have been sleeping on my new mattress for three nights now and today I have back pain. I'm not sure what I'll do yet but I most likely will have to get a different mattress.
I will update in a few days about what I do and what customer service is like.