impossible to cancel expire cellphone contract

My cell phone contract with Mtn expire 9/1/2016 and on 24/2/2016 I dial 808 to cancel my contract and move to prepaid so I can migrate my number to Vodacom and till today 14/3/2016 my cell phone is still working which means after 3 weeks my request after numerous phone calls and reference numbers Mtn had just ignored my request to cancel my contract and today I join Vodacom which means after very very very bad service from Mtn I had to get a new cell phone number because of them not cancelling my contract on my various requests since 24/2/2016