Cancellation fee ****

I want to do a premature Cancelation on my Vodacom contract that I signed up for HOWEVER WHEN I signed up for this contract it was under "promotion" for R300 unbeknown to me the ACTUAL amount is supposed to be R600 now because I am canceling my contract I am supposed to pay what the "ORIGINAL" amount was supposed to be at R600 pm!!!

This is completely ********* practice and just because your deals change monthly does not mean I should be penalized! I signed up for R300pm that's what I am Paying and that's the amount I want to be charged PM for my cancellation !!!!!