I'm really sorry to hear that your job didn't work out Audra, but at the same time, really glad to hear that you realised how stressful it was making your life and that you had the guts to bring an end to it. I can imagine it must be stressful trying to ring again. But honestly, if you ring and can't talk to her. Just write up a letter, date it, and post it to them as a formal resignation. You technically don't have to give them a reason, but you can give one. Otherwise, you can go in to the store to hand it in, because it's possible you may have to sign something anyway as an official termination of employment, I'm not 100% sure how that works

Seriously though, good on you for having the guts to do what was best for you. It can be pretty scary sometimes. I'm sure you'll manage to find something that fits in better with your classes and that isn't so stressful.