Every time I raise a new invoice, it comes up as Paid rather than a new invoice with a balance due. Has anyone experienced this before and any idea how I rectify this?

Hi there, goodness.

I can share some tips on how you can fix this.

It's possible that there are customer credits that we're automatically applied to the invoice that why it's showing as paid. To isolate the issue, you can go to the Account and Settings, then turn off the Automatically apply credits option. Here's how:
 

1. Select the Gear icon.
2. Choose Account and Settings.
3. Select Advanced on the left of the screen.
4. Click the Pencil icon in the Automation section.
5. Remove the check-mark in the box next to Automatically apply credits. 
6. Click Save and select Done.

After that process, open the invoice you've created and unapply or unlink the customer credit. I'll show you how:
 

1. Select Sales from the sidebar menu.
2. Go to the Invoices tab.
3. Locate and click the invoice to expand the view.
4. Under the Invoice activity section, select the View payment link.
5. Click the Clear Payment button.
6. Hit Save and Close, then choose Yes to confirm the changes.

Once your customer pays the invoice, it's time to receive the payment. Additionally, I've included an article that will help you track all invoices that are due on a particular date range: Report of invoices that are due on a specific day.

You can always tap the Community if you need assistance in accomplishing your other tasks. Looking forward to helping you out again.