Vodacom Retentions Lie

Called Vodacom retentions in December 2020 to cancel my contract which had expired. The agent by the name of Joy convinced me to stay and said he would give me a special package for a new two year contract. The package sounded very attractive and I agreed only to find that in January what was promised was not what I got. Now I can’t get hold of him to rectify this. Vodacom does not allow you to go back to retentions to sort the problem. Should I not receive any feedback I will go the legal route as I am left with an unusable contract.