Pay more for exactly same thing

I have a top up 55 contract with vodacom, this number *875 I purchase extra data, airtime or sms's for this number. I can do this with my Absa Account, *111# or myvodacom online. I have been purchasing through my Absa account for quite some time, I go in to prepaid select from Airtime, Blackberry Bundle, Data bundle valid 30 days, Data Bundle once off payment or SMS bundle. Today I tried the once off payment message received, contact your service provider this service is already activated. I go into myvodacom and see on this number I can buy prepaid the same as on Absa the difference is with Absa I can buy a once off Payment (1G x 12 months) for R899 (R74.91p/m) and with Vodacom it is R149p/m1G x 12months. This is a difference of R74.09 a month. I phone vodacom the message passed to me from Jason the team leader through Unati is that the Absa one only applies for Prepaid, he cannot speak to me as he is busy. How is it possible that I can purchase all other prepaid bundles for my top up number but not the cheaper option, and note this is in addition to my current contract value. This can not be fair or inline with consumer act?