unable to cancel my cellphone contract after trying for 6 months

I have had the worst service i have ever experienced from Vodacom. I have been a customer for the last 12 years and for the last 6 months i have tried everyday to cancel an old cell phone contract that i havent used in 4 years but i have been getting invoiced monthly for. i have spoken to countless people at Vodacom, sent countless of emails and i havent been assisted for 6 months. i am disgusted that i have been asking for help for so long and all i ever do is wait my life away on their ridiculous customer care lines all day everyday.