Autopay refund

I would like to request for a refund for my pre-paid plan. At the beginning, I had signed for a mobile number and opted to use autopay. Before the end of the month, I joined a multi-line account. At the end of the month, I was charged for my line twice (once through autopay and again through the multi-line account). I believe this double chrge is unjustified and therefore would like to seek a refund on the autopay payment. 

I look forward to communicating with a customer service officer with regards to this case. Thank you.