Cancel prepaid card
I recently travelled to US and bought a prepaid card, now I've returned to Melbourne, Australia, but just realised I've been charged another $40, so I think it's set up as auto-charge, and I need to stop it. I know I can contact my bank to block the credit payment but I'm a bit worried that I'll get some dishonest record in US, so I'd like to ask if there's a better way of cancelling the service.
When I bought the number in an AT&T shop, I got a mobile phone number (starts with 907), a card with text "Rethink Possible" on top left, there's an "RS#" number, "SKU" number, "UPC" number as well as "ICCID" number. I don't know what's needed and who should I contact in order to cancel it?
I tried to register for an account but the website shows prepaid cannot register something account.
Thanks a lot!