Freelance worker for a marketing agency/ No contract signed/ Charged for tax and other benefits.

Hi! I don't know much about taxes. When I was a regular employee, I was very lenient at checking how my taxes are computed because it is automatically payed by my employer. I only had one employer and Im still currently registered to their RDO code. I resigned last May 2015 and have not provided any form of contribution to BIR, PAGIBIG, SSS, PHILHEALTH ever since. I became a freelance model for different agencies, and accepted net payments right after every project. Some would collect BIR, PAGIBIG, SSS, PHILHEALTH information from me, but never did I receive any notification that part of my talent fee will be deducted because of these until I worked with one marketing agency who, at first, made me a buffer for one specific project. Im not registered as a regular employee at their agency. Never did. Did I sign any contract? No, Never. My first project (One day, I was promised 1,800) but I got it two weeks after from their payroll. I saw my payslip with deductions from pagibig, sss, philhealth and bir. I still got the net pay promised. the next project was 1600. No complaints. I was payed right after. The next project I was payed 1800 right after. But the previous one, is what I would like to complain about. I have a record of our conversation that our pay will still be 1800. After working with them for 6 days consecutively, They have informed me that I am only supposed to receive 1300 a day because of some budget restrictions of their client. BSC they call it. They said my first week (6days) "inabonohan na nga lang namin yan e". My second week which I worked for 4 days I will be payed 1300 a day. All of these changes, I was only informed of at my last day. Little did I know, when I was about to get my payslip for the first week (6days) I was expecting 1800 a day (as they said, "inabonohan lang nila yon") I only got a net 1600 a day because of the deductions.


First, If Im not a self employed individual how can they charge me for my withholding tax?
Second, Is there anything I can do here?