Vodacom does it AGAIN

Last year I got a bill from Vodacom for almost R10000 for data usage. After being under the impression that I signed top up contracts. Long story short, after a long fight they sorted it out. To my surprise this morning, I phoned Vodacom for something else and they told me, by the way, you have high usage on data. I was so stunned as I thought all my contracts was on top up after last years problem and I did change all the contracts to top up, last year. Now they say I upgraded my phone and migrated to the the open plan. I did upgrade, but made sure that I remain on the top up plan and the lady promised me that it was. I will not pay a sent on the extra data> I am really getting fed up with Vodacom's service, after being a client for 14 years now.