How can I manage a pre-paid account without a conventional phone?

I have purchased a prepaid SIM card to use in my residential security system as an emergency backup.  My security system does not have a key pad or a display, it is a self-contained system that automatically dials out when an emergency or security violation occurs.

I would like to establish an on-line account so I can monitor the usage of the account, refill the account balance and other management tasks.

I was told that I should use the last four digits of my account number as my PIN when I first log-on to set-up an account.  When I did that, the web site said it was sending me an SMS text with my new PIN.  My security system is unable to receive or display text messages so I have no idea what my PIN has been changed to nor how to change it to something I can use.

Please tell me how I can create an on-line account to manage my pre-paid account without a conventional phone.

Thank you.