How can I not get a R950pm contract if I’m currently paying R900pm

I’ve been with Vodacom since 2014 and received an sms last week saying that I can now upgrade. I then went to the iStore to upgrade from my iPhone 7 Plus which is currently on a uChoose 200 package and I pay R890pm to a iPhone XS Max 64GB on a 36 month contract at R950pm but was told I can’t as my Vodacom credit allocation is lower than R950. How can that be if on average I pay about R900 pm and have been for 2 years. I then called the contact Centre to ask but the consultant was more interested in talking to he’s co workers and muted me half the time and then just said I should go to the store. I’m really frustrated as I have been happy with Vodacom to be embarrassed like this.

How can I rectify this as 3 month waiting period does not make sense as my contract ends in 2 months, so then I might as well change to a different networ who’s willing to give me the phone.