Elite Rentals False Late Fees due to online payments Killeen, Texas

I made my payments on-line thru PSC for 6 months.  On the 7th month I received a letter saying I didn't pay my rent.  When paying I log on with my username and my own secret password and then pull my address up from a drop down menu.  They said my payment had posted to the wrong address.  From what I understood, they fixed it.  It then happened 2 more months.  When I received the receipt via email I never read the whole thing.  Just assumed it was paid.  Come to find out the computer system screwed up and someone had changed my name under my email address and password and was posting my payment to their account.  I was charged $400 late fees due to this.  They claimed they were helping me out and refunded $149, but still continued to tack the late fees on.  Even though I had paid my rent on time, since someone breeched the system it wasn't posted on time and they told me it was my fault because I didn't read the address on the receipt.  If I used my username and password and a drop down menu, why would I thouroughly read the receipt if it was emailed to my account, the money out of my bank account and an employee telling me each month that she fixed it.  I am a single mom of 2 in nursing school with no steady paycheck coming in and cannot afford this.  Go after someone who really doesn't pay their bills.  Maybe I should have caught it earlier, but I don't feel it's right to take my money when I tried to actually pay.  My neighbor who also rents from them has received an eviction notice twice and had to take her receipts to show them.