When you void a shipping label that had included Shipsurance (our optional discount insurance), you will immediately receive a refund to your Shipsurance account. If you reshipped immediately after or before voiding the labels, the credit may not have been applied to the new labels, leaving a large balance in your Shipsurance account.
Head to your Account Settings (the wrench icon in the upper right).
Next, select Shipping and then Carriers & Fulfillment from the sidebar on the left.
There will be a section for Shipsurance Insurance, this will show your Account Balance.
In order to use Shipsurance, you need to have a funded account (similar to Stamps or Express 1) from which to purchase insurance. As you process additional shipments with Shipsurance, the charges will be deducted from this account.
If you don't think you are going to use these funds in the next week or two, you can request a refund to your card by opening a case with ShipStation Customer Support.