nextCancellationDate is the next last possible date to cancel without renewing the subscription. There are three possible outcomes:
1) If no cancellation notice is set or we're within a free trial, the
nextCancellationDate is the end of the current period.
2) If we're before the notice period,
nextCancellationDateis the end of the current period minus the cancellation notice:
3) If we're past the cancellation notice,
nextCancellationDateis the end of the current period, plus another period, minus the cancellation notice: