Unfair billing

When i went to upgrade, I asked if i would be able to use the R200 i got to purchase data and use for calls, the saleslady at the pavillion store in westville said i could. I now purchased the bundle but my airtime hasn't been deducted, but is going to be billed to my account. As it is the lady said i only have to pay for my old phone in jan plus expect a pro rata billing for the new phone which i was ok with but when I phoned vodacom the other day to find out about my contract they say I have to pay till April! My budget did not accommodate for paying for 2 phones and now this extra billing for my data!!!???? Vodacom must needs to accommodate me now as I have been a lotal customer for years!!