He is forcing me to keep my contract

I called customer services last night asking to cancel my contract & the gentleman that helped me advised that I call in today. I called spoke to Mohamed, explained to him that I want to cancel my contract, I was due for an upgrade on the 19th of Jan, I want to keep my number, he then gave me options of the new specials which I said to him that I am not interested. I then asked him to keep my number as prepaid but then he said if I cancel I will loose my number. I again explained to him that I have had this number for over 8 years & I don't want to change it, he again said that is unacceptable but now he is not giving me reason why its unacceptable. I then explained to him that I ported to Cell C from Vodacom if I cant keep my number under Cell C then I rather port back to Vodacom. he said with attitude in his voice that he will put me through to the porting department, he then put me on hold not through, the next thing I know he hung up me. I am not pleased by his service & I rather port back to Vodacom than keeping a contract I don't need just to up sales.