Mtn worst service and false advertising

Mtn and it's false advertising i paid an upfront payment of R416 & I was told I get a free to use router plus pro-rata & payment for the month ahead which is April. Today I received a statement & it says I must pay R650 I called customer service I asked why must I pay that amount as the contractual amount is R269 and the extra fees were already paid. The customer service said they don't knw why I was charged a fee of R416 because the full amount I was suppose to pay was over R1000, I asked how because I was only informed of 416 now I must pay money I don't have. Instead they send me to the sales department that did not disclose all these hidden costs & I cannot even get any help