Maybe you'll need a bigger dish, the decoder should be OK

Since 1st October, DSTV switched from the Intersat satellites, IS10 and IS7, to a new satellite, the IS20 which was launched this year. Here's the link on that:
http://www.bizcommunity.com/Article/196/66/80920.html

This page shows the beams to various places. Now although the satellite is somewhere between here and India and you are closer to it here than in South Africa the intensity of the beam to this area is less.

http://www.intelsat.com/flash/coverage-maps/sat_foot.html?sat=IS-20 at 68.5%BA E&display=map&sp

Click on the KU-band EU/ME/Central Asia and you can see that it's intensity is 49dbW, click on the KU-band South Africa and it is 55.7 dbW. In general terms, the weaker the signal, the larger the dish needed.