The start of your project's billing period is determined by the day on which you enabled your first service. This means if another service is enabled three weeks into the billing cycle, it would be unfair to charge you for the full month seeing that you will have been using the service for a bit over a week when the billing period ends and invoices are generated.
Yes. Simply flip the "renew" switch in your billing overview and the service should be reinstated. Note that you will be charged as if it was enabled for the whole billing period it is re-activated in.