Initial sign in from abroad - need to cancel AutoPay!

I set up my prepaid plan in California and was told I could cancel AutoPay a couple of days before the end of the billing period. However, I was not told I couldn't do this from abroad (despite telling the sales associate I would be abroad for this) - the number has to receive a temporary password for me to be able to sign in for the first time (I tried inserting the SIM card, it does not work in Prague). I am not going back to the US for another 6 months and I will not be paying for the prepaid plan the whole time. I can't even call the help line from here and I didn't find an email address I could send an email to.