Can They Do This To Me? Is This Even Legal?

I've been with this company for a little over 6 years. I recently came back from FMLA leave as I went to care for my father in Las Vegas who had terminal cancer and only had 6 months to live as I was notified during the 5th month. I let my job know that I was back and they wanted me to return to work ASAP and my return date was Oct, 1st. I explained that I was still planning a ceremony for spreading my dads ashes in the ocean, and they said to just come back and then I could take a day off to handle that.
I returned to work a few days later and after two days of work, my dads passing finally hits me and I became really depressed and unable to work, and I called in sick for the third day, fourth day, and fifth day. On the fourth day I was in a rather hostile situation with so called friends. With all the drama I experienced in Las Vegas and then coming home to find out my fiance doesn't want to be with me anymore really causing me to be mentally unstable. Long story short, I woke up with my phone at 1% of battery and I slept at a friends place so I didn't have my charger. I have two phones with me and both of them were dead with no charger. Meanwhile I didn't think I needed to call the store because texting my boss used to be good enough before I went on leave. So I text my boss that I would need a few more days to find out what was going on with me. When I finally got home and was able to charge my phone I got a text from him saying I was suppose to call the store and that he wasn't working. I called the store a few hours after my initial start time and they said that I was a no call/no show and the next day was the same except I called the store right around my start time just to make sure they knew I wasn't coming in and the customer service lady said thats okay because Dan already called Daniel to come in. I was later told that I was considered a no show no call again. I went in to work the next day to find out that they took me off the schedule and to wait to speak to HR about all this.
I corresponded with HR through calls as well as text for the next week and then I didn't hear from them over the weekend and missed their call on that monday, then finally get a hold of HR today (Friday) to find out what was going on and they tell me that I resigned and to pick up my separation package. Is this even legal? I also explained that I needed my job because I had to find me another place to live. Knowing this why would I resign and forfeit unemployment?
On a separate note, before I went on leave I had just graduated from college. While I was going to school, my store director and his other employees were harassing me and it felt as if they were trying to make things hard for me so that I would quit. I was accused of a lot of petty things and I can recall alot of the different scenarios and what was said to me if needed. Thanks