In-text: Statistics South Africa (2015) published ….  or, if at the end of the sentence, for example: Population growth …. (Statistics South Africa, 2015). 

Reference list:

Statistics South Africa. (2015). Mid-year population estimates, 2015, P0302. Available from: < http://www.statssa.gov.za/?page_id=1854&PPN=P0302&SCH=6334>. [Accessed on 28 July 2015].