Bad service from vodacom

My Vodacom contract ended December 2025 .January 2026 I called the vodacom customer number and I asked the consultant to cancel my contract and he told me my contract will end 28 February2026. February i received a call from vodacom about an upgrade.i told him i have cancelled my contract ,he said it is not cancelled.I called vodacom again i was told my contract is not cancelled and it will be cancelled 31 march 2026.Why am I being charged for vodacom employee's mistake.I received poor service from vodacom.