Not keeping to agreement

I am a Vodacom customer going on for +/- 20 years.

About 10 years ago I wanted to cancel my contract and move to another service provider as the deals were much better. When I called in to cancel my contract, I was transferred to the RETENTIONS DEPT. This department worked on a deal to RETAIN me as a customer. The deal included a recurring 5 gig incentive data that was to be added to my account every month.

This has happened without any issues, including when I upgraded multiple times, the 5 gig was always added to my account.

My last contract was taken over 36 months, so when the consultant added my 5 gig during the upgrade, she advised that the time period has to be 24 months, so she will load it for 24 months and when it expires I must call in for it to be re-activated.

I have reached the end of 24 months and I did call in to get the data activated to which I was told that it cannot be done and that I would need to upgrade or renew the contract to get the bonus data deals that come with new contracts. The incentive data that was promised to me to retain me as a customer did not have any such conditions,

I do not agree with having to either upgrade or renew at this time. All of these arrangements/agreements will be on record - so how can it not be fulfilled?