Get your act together

At this point I'm just board of Vodacom if I got a contract 1 that is R349 a month and the other 1 is R299 a month with addittional insurance that works out to R50 and it suppose to work out to R698 , how is it that I get bills of R800/900 a month how is it possible that a network advertises something at a certain price and then changes the pricing after a few months seriously what is happening there?????