MONIES DEDUCTED FROM BANK AFTER CANCELLING CONTRAC

I contacted Zane in Retentions 4 March 2015 to get an early cancellation quote as we were moving to Australia. He gave me the figure of R3083.23 which included the current invoice for March of R1095.10. He advised if I paid this amount the contract could be cancelled. I paid in full and emailed proof of payment. I received an email from MTN 17 March to confirm receipt and asking me when to cancel contract to which I said end March. MTN have debited my bank account in April for R1519 - invoice they emailed says for data usage and April subscription - I queried this as my contract was supposed to be cancelled end March - no response. I have now received an invoice for May for subscription costs. I have again emailed - no response and fear they will just deduct out my bank account again. I did not go over my data usage in March I had a credit limit on my account and I had personally checked on 15 march with Precious MTN customer services who advised we still had over 5 gigs available. We stopped using the wifi 18 March when we flew to Australia. MTN are ignoring my emails and just deducting monies from my account. PLEASE HELP. I tried calling from Aus was on hold for 15 min