withholding part of my deposit.

My argument is, I moved in on the 20th of October 2015 in one of their complex and I was allowed to pay half pro rata rent r1166.66 and admin fees of r900 and deposit of r 5250. As agreed with the previous Agent(Wayne ) and the agreement was I will pay on the 15th of every month since I get my salary on the 15th . and he was only to happy with that. Now when I move out on the 31th March 2016 due to serious personal issues I paid half of my rent(1750). AND now this new agent by the name of (Stefanie ) is charging me a full rent amount, but I stayed in the flat for only 15th days from my last full rent amount on the 15th of FEBRAURY and to top it, a new tenant moved in on the 1st of April just after I vacated the complex... so there where no damages whatsoever and I have pictures taken to proof that ... according to me , my move out date was on the 15th of April, that would have been a full month and that when I would have been liable to pay the full rent amount... Stefanie is now holding my r1750 from my deposit ...... please assist a widowed mother of Three.