I work at a smoothie bar, hate it, what's the best way to quit?

I have been working at a smoothie place since 14th of December. I am 19 years old and a full-time college student so this is not some serious career thing...just extra cash. My boss is overbearing and has serious 'tude. The actual place where I work is dirty. It smells weird and there is one dishrag which is used to clean the entire place. Any leak, any spill-over from a customer's cup, any spot inside the fridge - all cleaned with the same rag. Each day the rag is changed, but they are all nasty old rags. My boss has had me working 40 hour weeks, 8 hour days, and this is CHRISTMAS BREAK. I have yet to see a paycheck. This is a franchise btw. My boss won't stop calling my cell phone to get me to work. If I am lucky, I get one day off a week, otherwise I am working a 5, 6, or 8 hour shift in this hellhole. He also pays $5.75/hour, very low wage for my state. How do I quit this job with dignity and get my paycheck from this boss-from-hell? I hate confrontation...