Im so Sick of Vodacom

I constantly have issues with Vodacom I have been on a contract with them for 4 years now , I was promised if I change my debit order date I wont get double debited , I knew off paying in advanced that why I kept asking the lady if she is sure i wont get double debited and she kept saying she is sure , just to find out 2day i was double debited , I phoned spoke to a manager and was told shes sorry I need to reverse the premiums at the back now its inconvenient for me because of untrained staff i just want to cancel my contract with you guys after 4 years and im still so unhappy with Vodacom i wont recommend you guys to any1 in the future