Vodacom Upgrade Contract over the phone by decreasing the Airtime

In May 2018 Vodacom contacted my wife RE Botha requested that Vodacom want to change the Amount of airtime from R220 to R200, because the R220 (Uchoose Package) no longer existed.

No mentioning of any upgrade was made. My Wife and myself was due for an upgrade in May 2018, but we decided that our existing Mobile Devices was still in good shape and therefore no need to upgrade.

My Mobile Device started to give problems, so I decided that I need to upgrade. When I did an Online request I was informed that I can only upgrade in May 2020.

My question is? Vodacom requested over the telephone to Change the Airtime Quantity. No Forms or Contracts was sign. Is this valid as no Documents was signed.

When I do an Upgrade, I have to sign and my wife have to sign to. My wife is the main Contract Holder.