Upgrade fail due to low credit

I am due on my cellphone contract for an upgrade. Now when I wanted to upgrade and find out if I can still stay on the data package instead of airtime I was told I do not qualify because of a low credit score. I do not understand this, the contract I want to take up is R300 cheaper than what I am paying now. I have never skipped a Vodacom payment and now I have a low credit score. I have 3 contracts with Vodacom. 2 which they upgraded only the data deals 2 weeks ago now I cant??? Guess I will wait until May until this contract ends and change to another service provider!!! I will also take my other 2 cobtracts to another service provider when they are done! Just a pity someone phoned me and renewed those 2 for another 24 months When they phone you they sell products as they please but when you phone them they have excuses! Can't even miss a payment as it goes off by DEBIT ORDER