Employer refusing to pay earned wages

I worked as a receptionist for a certain company for 2 weeks before quitting to find something better. The pay period is bi weekly and after my first week there, that Monday was their payday. I was expecting to receive my first check on that day and when at the end of my shift I did not get a check I asked my boss if I was getting paid that day. The answer I was given was "oh didnt we tell you that we withhold 1 weeks pay as a deposit". I told them that they never informed me of such a policy and that there was no way that I could wait 3 weeks to receive my first check and lose my first weeks pay. The boss told me that they were going to pay me some of the money and withhold $100 and they will do that every pay period until they have a full weeks money for their deposit. I was very upset about this as I am a single mom and coming home with even 100 dollars less every 2 weeks is a big deal. The next week I worked 2 days and had fallen ill for 2 days and did not come in. The 5th day was x-mas and the company was closed. The following monday (after a long weekend of thinking) I decided to quit. Basically they owe me for 2 days plus the 100 deposit. The employer is refusing to pay me saying that their policy is if you do not give them 1=2 week notice you lose this money. I have been corresponding with them by email for the past week to no avail. Now they are saying they are investigating me (for what I have no idea) and I can no longer email them or call. I must only communicate by regular mail. My question is do they have the right to withhold this money from me? What should I do? Also would they have to also pay me for the day they were closed that week which was my last week? Do they have the right to tell me not to email or call? I am a single mom and really needed this money and now am left with not a dollar to my name. Please please help me. I do not know what to do or how to handle this situation.