Account Cancelled in Jan 2016 and still being bill

Good Day, <br> <br> I have just received a bill for a land line that I had cancelled in January the 06 2016. <br> I called today to ask them to please rectify this and reverse the charges only to be told they cant because they never cancelled my line??? Who's fault is that! I have the acknowledgement email! <br> Your incompetence is not my problem. <br> <br> This needs to be fixed as I refuse to pay for services that have not been used since January.