Poor service

I have cancelled my contract at the end of February 2016. I had requested a letter of cancellation with the amount required to terminate my contract, Payment was made in full with no outstanding balance. I had my cell no moved to another cell provider. I didn't receive any statement in March, But I have received a statement of an amount that has to be paid for the month of April . Since last week I have been contacting Vodacom to assist . I was transferred to the accounts department and explained the entire story, the consulted then transferred me to the new 3D department, according to her this was a priority department for better service to clients and the person that I should speak to was Nkululeko. At the time he/she was busy but will call me back in 30 min. Nothing happened, I called back later that day with the same result. I have called them 3 times this morning with no result