Incorrect invoice

i have reciebed my invioce where i advised i need to pay c=vodacom r905.37 for my contract <br> <br> According to what i have signed i agreed to pay R685.00 as a monthly installment <br> <br> i will not to continue with this contract and return back the phn <br> <br> if this is not fix with in 2 days im logging a complaint with the ombudsman<br> <br> i didnt agree to this when i entered into a contract with vodacom for line ***<br>