month away from us

I am not gonna use my prepaid line for a month or two, I am out of the country so I am not able to call without being extra charged here. My question is, if I don't pay one month, on the next are they gonna change me one or both months? Or should I block my line for that month ? I dont wanna make a mess, since at the end, how am I supose to unblock it without the code by imessage  to enter the website

I have a prepaid acount with 2 lines, if that matters