tmobile security deposit Nationwide

Chose no contact plan and monthly payment for phone. I was charge a $100. Security Deposit plus a down payment on phone. I paid off phone 3 months later. I asked about my security deposit see how the phone was paid off. The rep told me that I would be credited my security deposit after I was with tmobile for one year. If yr on a no contract phone plane why the security deposit and why do I have to wait one yr for refund this is not a contact phone plane. Then I was going to add a tablet to my account and they want another $100. Security deposit. Isn't something w ring here?