BAD SERVICE

In december 2015 I called and cancelled my contract I asked te agent would I incur any cost the agents I called in and spoke to told me I would not this on 3 occasions I settled what I owed and contacted them to cancel I sent a email as system was down there after It was fine about 3 days ago I get a sms stating I shud sort out my debt when I enquired they said I shud forward my cancelation email which I did 2day I called the contact center agent, after I eplaned that the line is no longer in use as of day1 when I received it they keep promising to activate it but don't activate, I've had enough I will not pay for monies which are not correct I will not be liable for there mistakes as I paid in full