VODACOM IS DISHONEST AND UNHELPFUL EVEN IF IT IS THEIR FAULT

I wanted to cancel my Vodacom contract, and when I phoned in I was presented with a attractive deal top up flexi account to receive R140 airtime a month, which took because its much cheaper than currently paying, and a better price was also given to the other number also on the same account. Well when i received the invoice for this month its all the same amounts as before. and now all of the sudden is a RED FLEXI account with 50min airtime???? AND WHAT A STRUGGLE TO HAVE THIS RESOLVED I WANT WHAT I SIGNED UP FOR WILL NOT PAY THIS INCORRECT AMOUNTS AND WANT MY R140 AIRTIME NOT 50 MIN CALL TIME.