Dissappointed in Vodacom afters so many years

I received a notification from Vodacom that I can upgrade on my contract! At first they didn't really have a package deal I was 100! satisfied with. So long story short I took a deal. After a week my husband upgraded for the same phone at MTN, paying less and getting more data and minutes. A few days ago my Vodacom bill came and it was almost R500 more than what I am supposed to pay. I enquired at customercare, they say that I still need to pay off my previous handset! No one informed me at my upgrade that I would still have 2 months to pay off the handset, thinking all is sorted as they said I can come for an upgrade! So unhappy with Vodacom, this is for sure my last contract with them.