debit order

My contract ended in May and i cancelled it in July, however i still receive airtime month end of July. I went back to the store in birch acres mall and i was told it was the last airtime and debit order. But to my surprise samething happened in August, i received airtime and i was billed too. Now the problem is that NOW on the 25th of September a debit order went through but i never received any airtime and i have never missed any payment with mtn. This IA really disturbing as i have been a loyal customer but they *****ing me and i had to run around waisting my transport only to find no help. Even today i was at the store assisted by Nondumiso but she still couldn't help me just told me that maybe i missed one debit order, of which this is a joke as i have NEVER skipped any payment. I just want my money back.