I want my money back

I made a purchase on 26.09.2015 paid with a bank card, the above mentioned cashier was assisting me, said the payment was declined and mentioned that maybe they were offline, she decided to try it again and it approved, later at home I realised I was billed twice according to bank notification on my phone, I called the store the following day, she told me it can only be solved if I bring bank statement as proof, I took the bank statement to the store on 03-10-15 one of her colleagues took it, wrote bank card number and my contact details on it, she told me it will be done the following day and promised to call me, I'm still waiting for my money to be refunded, I haven't heard from any one from this store when I call and ask to speak to the manager they keep me on hold and finally hang up, I want my money back I'm not prepared to waste more money calling this store or wasting petrol driving there, I want my money from these *********** ******.