Hidden upgrade fees

I went into the store at Melrose Arch and asked if I'm due for an upgrade. They checked and said yes. They did not inform me of any additional fees. Now on my January bill there is a fee of over R800 as a device carryover fee. If I knew about this fee I wouldn't have upgraded in the first place. I phoned and was told I upgraded in month 22 of 24. So why was I told I'm due for an upgrade?? Pathetic service.