Vodacom is holding customers hostage with their services

I'm extremely dissatisfied with Vodacom's service. Upon signing a contract with them, I soon realized that my data was depleting rapidly. When I attempted to cancel the contract, I was informed that it was not possible. After searching online for a cancellation number, I was told that if I were to cancel, I'd incur a penalty equivalent to the total amount for the entire contract term. Additionally, I was informed that resolution could only be sought by visiting the store and inquiring about their policy. However, upon visiting the store, I was simply told that cancellation was impossible. Am I now compelled to continue using unsatisfactory services or to pay for services I no longer desire? It feels as though Vodacom is holding customers hostage with their services, which is deeply disappointing and unfair.