Refusing to cancel my contract

<p>on the 6th of February 2017 I sent a contract cancellation form (same month that my contract expired) and i received a auto response email sort of acknowledging that my documents have been received. they said it takes 21 day for the cancellation to be processed, ok, on the 2nd of March I call to check if it has been cancelled and it hasn't , they say no I shouldn't have done it myself I should have gone to the shop, ok as their instruction I went to the shop, explained my story and they gave me a case number. 31st of March was the last day the sim card had network, as of the first of April I couldnt use the Internet check available data or to call 180 number. I don't get why yesterday I was billed, if I'm done paying for the phone and have a disconnected sim card why am I still paying, and without this 2 my contract with them doesn't exist so why am I still on their database</p>