Mistake or rip-off?

I recently received a call from a Vodacom rep, who offered me a special deal on a new contract. The deal was exactly the same as what I already had, but instead of paying R210/month, I would only have to pay R175/month, and as a bonus, Microsoft Office free for 2 years. So, I accepted the offer, and the rep said he would courrier the contract to me. I received the Office software, but no contract. Today I received my 1st invoice........R408.30 ***? I have been a Vodacom customer for more than 20 years, and this is how I get treated? So excuse me for being extremely ****ed off. Is this a mistake, or a deliberate rip-off?