In your dashboard, you can see how many Invoices you have created since you made your account.

Let's say that number shows you 10 invoices, but when you click on it, you can only see 6 documents. You thought you deleted them, but the number didn't change.

If this is your case, please do the following:

Go to Invoices, click on "Filter Invoices" and in the "Status" box, pick "Cancelled" and hit "Apply".

Now you can probably see the rest of your invoices, this is where they were hiding. You can select the Cancelled invoices that you want to delete, and hit the red "Delete" button.

TIP: Next time you cancel an invoice, make sure you do the same procedure to delete the invoice, otherwise it will still remain here and your Invoice series and number will not go back, unless you delete the Invoice.