Dubious upgrade practices

We upgraded my son's data contract on the 26 April 2024, and since the upgrade we have been unable to make voice calls, even when there's airtime. After 45 minutes in the store checking the sim they told us the contract was at fault. After 45 minutes on the phone to customer care they said the new 100gb contract doesn't allow calls. This was not explained to me at the time of the upgrade, and Vodacom has been more than happy to charge R10/month on caller ID for the "modem". Now we are stuck. No way to migrate or downgrade to our old contract despite being clearly mis sold during the "upgrade".