Unable to upgrade under debt review

I have been a loyal customer of Vodacom for several years now. Due to unforeseen circumstances, I had to enter debt review but my cellphone contract was not part of the review and formed part of my personal spending. I tried to update my cellphone contract a day ago to one that was nearly R300 cheaper than what I am paying for now, knowing it would be more affordable and better for the process because I would be saving more. I have never missed a single payment, even under debt review, yet I am being declined an upgrade. I am able to afford the payment for my contract, in fact, I know I don't stand a chance of missing one now because the contract I asked for is cheaper, why am I being denied?