Vodacom useless and dishonest

Vodacom has unilaterally changed my plan I am on. I am not under contract any more. They just decided to change my plan to a more expensive option without consulting me. I was on too high a plan and needed a plan with lower monthly cost and airtime. For 2 months now I am struggling to downgrade (upgrade) to a plan with lower cost and air time. The App is absolute useless as it will NOT process the upgrade and will return to home screen. I have tried more than 10 times to upgrade through the APP with no luck at all. I have spoken more than once to the call centre and that even did not work, It seems a deliberate effort from Vodacom to prevent me from downgrading. After you have gone to the whole process with the sales person you are told every time to please call another number. I do not seem to be able to get out of this frustrating circle with Vodacom and has now paid 2 months for 2 much airtime which they know well I cannot use at my current usage.