Distasteful experience from Vodacom and Cellucity

I would never advise my friends, collegues or kids to take any contract with Vodacom, no one cares to explain why my bill for June is R507, double the amount of the signed contract, after Vincent specifically told me that my account was fixed And I will only pay the agreed amount of R248,99, a contract is a fixed a month for a fixed term, I don't expect the amount to fluctuate