Billing

I had a neotel internet line installed a few months ago, i even paid installation fee and submitted my id and proof of address for me to get approved andi am sure money was deducted from my account for that months ussage as well I have cancelled my internet in April 2015 to take effect last day woulld be May 2015. Only to realise a june invoice was swnt and money was deducted. Now you are claiming that this was a mistake and that i am in credit but if i owe you money i must pay that, i want to know why???? Seeing that i paid via dwbit order every month and that my account was deducted correctly. Also i was told that this is as per my contract, note that I Did Not Sign a contract. I phoned regarding my debit order date and about the cancellation. Reason for cancel was that i am no longer in South Africa. I hadto give authority to my sister to phone on my behalf and according to you money was deducted due to neotel not doing what they were suppose to do and rhat is cancel my internet as per my instruction. I want my money refunded. I need this done urgently....