Go Phone current balance, how do I use it to pay for next payment?

I have a "current balance" of $86.70 on my GoPhone account. I stopped my auto enrolling last month. My next payment is due on 2-7-15. Will the amount of the plan I use ($45 plan) be deducted from my current balance? Or do I need to contact someone on the 7th to have it deducted?