New Sales Job changed how pay scale works

I recently was hired for a sales position. For two weeks I was told that I would be given a base pay if I worked 6 days or did 14 demos a week. I was to be payed weekly. Now I am being told that I will be payed weekly for any commission I receive from sales weekly and that I will only get the base pay at the end of the month if it higher than my overall commission for the month. I was also told that base pay only counted if I did the 14 demos, the alternative 6 days seems to no longer exist. They are giving me an advance to pay my rent, but nothing more. So in the end I owe them money it feels. I have worked 12 days and have done 3 sales, one which was cancelled. For both weeks that I worked I was not able to do 14 demos. I remember signing paper work for pay, but I was not given a copy. I wouldn't have taken this job if I had known that they were lying to be about how the pay was going to work for my position. I have other bills besides rent that I have to pay and I basically have no money at all. I feel trapped and miss lead. What are my options?