Reneging on verbal agreement

About 2 years ago I contacted the Vodacom call centre because there is a chronic lack of signal in our area. I explained that I work from home and need to have a reliable signal for my phone and for my data contract. The agent told me that Vodacom was in negotiations with a property owner to build a tower in our area but that until that was finalised I agreed to a 20% discount on my phone and data subscriptions. This has been in place for more than a year but when I realised that when I renewed my data contract a few months ago, the discount has been removed from my data contract. The verbal agreement is legal and binding and until the tower is in place and the signal improved, the discount needs to be app**** to both the phone and data contract. I expect this to be rectified with immediate effect and the overcharged amount for the past few months to be refunded to me, failing which I will pursue legal action.