mtn contract cancelation

My data contract expire with this company and its due for upgrade which I don't want to perform, been trying to call them on 135 to cancel the contract but u will hold for more than 1hr without any response but the moment you get fed up n try their upgrade line they pick it up within seconds which is totally puzzling to me when I wanna cancel they don't pick but when I wana stay they pick ,which I find to be totally uncalled for, I no longer want the contract and its my choice .