Security deposit refund

I have been staying in this building for the past 5 years,I have been paying my rental in full, 06 January 2018,they gave they gave us notice that the rental is going up by more than 6-10%,the very same day I typed them a text saying I am moving monthend of January as I cannot be paying so much of rental for a ***sty.They came to do a dual checking and no fault was found.I had paid them a deposit of R3400 in 2013 when I moved in .To my surprise they only refunded me R1959 and when I queried this with the caretaker he told me that the City Council has been in arrears,and as a tenant I strongly believe that City Council being in arrears is not my fault at all as I have been paying my rental in full monthly.On the 20th February I went to the Housing Tribunal to query this,they wrote them a letter to say the need to respond within 7 days and they never,I laso submitted to them an original letter and they chose to ignore it