Help me understand Committed Used discounts (CUD) as it applies to Cloud SQL instances

[dheerajpanyam]

Problem Statement:- We have been running a single active Cloud SQL instance along with 3 other stopped Cloud SQL instances. We signed up for 1 year CUD for Cloud SQL.  I see that our August bill included some kind of promotional discount.  Fast forward to September and our monthly cost doubled to $243 with nothing changing in cloud sql instance and also no new instances provisioned.  Surprisingly the on-demand pricing for the instance is way cheaper than CUD.

Below is my reasoning please let me know if this is correct

We must have signed up for CUD for a higher Cloud SQL instance size and somewhere down the line downgraded the instance and since consumption is less , we are charged a penalty so to speak.

Below are the monthly Cloud SQL costs by SKU for Aug and September. As you can see we received some form of promotion for August not sure what it is , but same is not present for Sep

August Cloud SQL CostSeptember Cloud SQL Cost