By mistake opt for few services , Now getting billed heavily every month. How to know that you have stopped all instances and storage for your account?

The billing forecast is just that, a forecast. It's the 3rd of July today, so it looks at what you have run for the first two days of this month and then multiplies it by 15.5 to give a prediction of what things will look like by the end of the month.

If you have stopped and terminated all your EC2 instances then you will no longer be billed for them the moment they were terminated.

Make sure that you have deleted all EBS volumes that were attached to those instances (they may have been deleted anyway, but depending on the AMI some may not have been). And delete any snapshots you may have.

If may appear rather drastic, but consider AWS Nuke if you want to ensure you have nothing at all accruing any charges in your account.

You can also check AWS Bills in AWS Billing and Cost Management console. The Details section shows all the charges incurred by various AWS services on your account.