Vodacom premature upgrade with never ending proble

In 2013 I went to Mokopane Vodacom shop and I asked when I could upgrade they told me I qualify for a premature upgrade for an iPhone 5s. My original contract only expired in August of 2014. Now that I have finished my 24 months on the handset and would like to upgrade to an iPhone 6s they then diverted me to the call centre. Now When I phone the call centre they just tell me sorry I have to wait until August of 2016. So even after paying my bills every month on smart xl I can only get a new phone after 3 long(premature) years. Will definitely think twice before renewing. Bad selling pitch to customers.