Try to not panic. It will all work out fine because Fiverr customer support will be able to see if there has been a payment problem and they will reimburse you.
You may not be aware that at the point of ordering, your funds do not go to the seller, so they are held safe even if it’s a massive headache to have them missing from the bank.
They are held in escrow by Fiverr, and stay in escrow until the seller has delivered a satisfactory project. If the seller has indeed not received an order (and if the payment was duplicated also), you will receive both payments refunded–or maybe customer support will assist you to place the order you hoped to have made.
I think Fiverr will respond quite quickly to this. I hope so.
If contacting your bank, be very careful that you do not mistakenly pull funds back from Fiverr if there is any chance an order WAS placed–this could result in you losing your Fiverr account because that could come across as a fraudulent purchase.
So the safest method of redress is first of all via Fiverr Customer Support using a help (support) ticket.