Complaint on *** cellnumber

I took a cellphone contract from MTN in March 2013 which expired on 13 March 2015. I was paying R400 per month through debit order. After the contract expired I called MTN and enquired what is going to happen e.g do I need to cancel the contract or it will automatically be cancelled and I was told that if I don't cancel the contract they will only deduct R175 for airtime. To my surprise on 1 April 2015 R400 was deducted. On 1 May 2015 again a R400 was deducted by MTN from my bank account. After that I called them and enquired and I was told that I will be refunded. Because I was angry I cancelled the contract and changed to prepaid. For the whole month of May 2015 I was on prepaid but MTN deducted R375 from my bank account on 30 May 2015.