Exploitation

In January I did an upgrade on my Vodacom contract. My previous contract was 22 months old. My new cotract was R200 according to Vodacom booklets and Vodacom agent..I was told that they will add R60 for two moths on top of my R200 premium for two months.. But they decided to add R84 instead of R60.. What I don't understand is that where is the additional amount coming from... I contacted them via customer care but they failed to assist me.. What kind of exploitation is this and why would you exploit your loyal customer.. I hv been a loyal customer for years... Today they hv proved to me they are really failing as a network..