Vodacom's harmfull business practice upon contract conclusion

Vodacom has a harmful business practice with regards to contracts that run out. The contract is entered into at a fixed price and duration. Vodacom does not stop providing the "service", nor notify you that the contract has run out. They then to proceed to claim maximum rates and keep on the providing the service. This unilateral "extension" of the original contract is therefore null and void due to the agreed to essence of the contract being altered, namely term and rate being being altered by Vodacom. There is therefore no meeting of the minds regarding the "extension" and it is therefore null and void in terms of contract law. Notwithstanding that, Vodacom still entitles themselves to exercise their 30 days cancellation clause and other terms and conditions.