Being charged after cancellation

As of 27/02/2016 I have cancelled my policy with Momentum STI (this was done via me calling the call centre, the call centre agent told me that 26/02/2016 will be my last official day of cover). I was however, charged at the end of February and charged again this month! I have sent 3 emails to the provided email address over the past three weeks...no response. I have called the call centre a few times and cant get through (Sometimes the agents just transfer me to a dead line). I am now being charged by Momentum AND my current insurance provider each month. Please review your recorded telephone calls logged to my account MT***8. How is it possible that your agent can say to me on the phone that the 26/02/2016 will be my last day when CLEARLY I am still being charged (2 MONTHS AFTER THE FACT). The premiums that have been deducted need to be refunded to me. Momentum has served me well for my duration of cover with them, but the moment that I leave, they drop the ball? come on guys. For an organisation as streamlined and professional as Momentum show themselves to be, this is utterly ridiculous, impossible to get any communication with you guys.