Started a new RDS instance, and fees went ballistic (well, nearly) for some reason?

Created a new RDS MySQL t3.micro server to use for development purposes and testing. Total cost is supposed to be $0.026 per hour for a Standard, Single-AZ instance of this type in my selected region which means around $18.72 per month.

For some reason, my billing graph shows an increased cost of around $13 PER DAY since I started up the server?

I have shut it down temporarily, but does someone know what could be causing this? No other changes have been made to my AWS environment.

UPDATE: It seems APS1-RDS:PIOPS jumped for some reason, and I'm not sure if it is related? Even though the DB is shut down, the billing is continuing?

If you stop an RDS database, only some of the fees stop.

The cost of the EBS volumes that store your data will continue to accrue even if the instance they're attached to is not running.

In your case, you chose a high-performance storage option (Provisioned IOPS SSDs), which dwarves the cost of the instance running, so by shutting down the instance, you didn't actually reduce the cost significantly.

Switch the volume to a more reasonable GP2 or GP3 volume and the costs should go down significantly. Almost no dev-System will need provisioned IOPS SSDs.