Libby Stockwell

We signed up for professional account on the understanding that when creating a task and setting a due date it would alert our computer / phones on the due day and time. it doesnt seem to go into an alert it just is in the notification bar when we look but only sometimes not every single one, but doesnt go off like a typical notification you would receive or how a calendar task would flash on the phone or computer. how can i get it to actually alert us on the due date?