Miss led by the Vodacom inarticulate sales person

I have been a customer of Vodacom probably since they began. I renewed my contract with Vodacom early July. They insisted that I should receive a free phone and tablet as it would save me m.oney and I was told it would increase data etc for two phones and a mini modum and the cost would increase from R409 a month to R530. I had told them that I didn't really need a new phone but they insisted it would save me money. Everything duly happened and I was happy until I received the account yesterday for the end of August for R810. I immediately phoned them and was told that someone would phone me today.....which didn't happen. I phoned about an hour ago and eventually got put through to somebody who put me through to somebody else. The upshot of the conversation was that if I had returned the phone etc in July then they could have done something but it was too late. Remember I only received the statement yesterday and was misled as to the total cost per month. Effectively they are not interested even in an old customer. I am not sure what to do next...speak to my attorney, sign a contract with MTN and wait for Vodacom to sue me for arrears and contest it on the grounds that I was misled by their sales person which they obviously wouldn't admit. How does one deal with such impossible people? I might have been a customer for a long time with no complaints. That obviously counts for nothing.