I've set my prepaid on full automatic top-ups, so my experience may not exactly paralllel yours. If you have selected a monthly add-on through the web interface, you are given the opportunity to select auto-renew or renew each month. If you selected auto-renew then it will do so, as long as there is sufficient cash in the account to cover it. If you just renewed forthe month, then you would need to select again.
I suggest you connect with Telus ASAP and get your login sorted out, as the web interface is without a doubt the easiest way to manage a prepaid account.
Here is the view of the section of the web interface from my account:
As you can see, there is a choice to renew automatically, or renew immediately, which would reset the date of the next renewal.
Hope this helps!